The former two-time world heavyweight champion, 36, was travelling in the back of a black Lexus when the SUV hit a stationary truck on a busy highway in Makun, Ogun State.
He suffered minor injuries and has been taken to hospital for treatment, while two passengers in the vehicle died, according to authorities.
Two other people escaped unhurt, said the Nigerian federal road safety corps (FRSC).
A total of five adult males were involved in the crash, it added.
The Ogun State government said in a statement that "preliminary reports indicate that two male foreign nationals died on the spot".
Joshua is on holiday in Africa following his win over US YouTuber-turned-boxer Jake Paul in Miami just over a week ago.
The crash happened on the Lagos-Ibadan Expressway near Sagamu, around 30 miles from the country's largest city Lagos, at about midday local time (11am UK time), according to the FRSC.
How did the crash happen?
The corps said preliminary findings indicated the Lexus was "suspected to be travelling beyond the legally prescribed limit" and "lost control" while overtaking before crashing into the truck, which was parked by the side of the road.
"The primary causes of the crash being excessive speed and wrongful overtaking constitute serious traffic violations and remain among the leading causes of fatal road crashes on Nigerian highways," the FRSC said on X.
Lanre Ogunlowo, the police commissioner for Ogun State, said: "Anthony Joshua is in an undisclosed hospital being treated for his injuries." He said he has no further information on the injuries.
The boxer has Nigerian heritage
Joshua, who is the son of British-Nigerian parents, attended a boarding school in Ikenne, around 50 miles from where the crash happened, before returning to Britain at the age of 12.
Pictures released by the FRSC show the badly damaged Lexus that Joshua was travelling in and the red Sinotruck that it collided with.
'Wincing in pain'
Footage posted on social media shows the British ex-world heavyweight champion apparently wincing in pain as he is helped out of the wreckage by a crowd.
Other clips show him in an emergency vehicle, wearing only a pair of shorts, as he is driven away from the scene.
The FRSC said: "Two persons sadly lost their lives, one sustained injuries, while two others escaped unhurt.
"Anthony Joshua was rescued alive and sustained minor injuries."
Investigation under way
Police said in a statement that the two people who died have been taken to Livewell Hospital Morgue, in nearby Sagamu, while the circumstances of the crash are "currently being investigated".
"The Ogun State Police Command extends heartfelt condolences to the families of the deceased and assures the public that a thorough investigation into the circumstances surrounding the accident has commenced," a statement said.
The crash happened just days after Joshua knocked out Jake Paul in the sixth round of their 19 December bout.
The fight marked the end of a 14-month hiatus for Joshua, who is expected to fight long-time rival Tyson Fury in 2026.
The Mar-a-Lago meeting did not materially move things forward but nor was there a bust-up like that Oval Office moment in February.
There were however some notable takeaways.
First, Zelenskyy's facial expressions.
At times he looked exasperated - like when Trump made light of a profoundly important negotiation by talking about the Mar-a-Lago food and the physique of the Ukrainian leader's generals. Playground stuff.
There was a memorable moment when Zelenskyy's poker face fell away. He shrugged, then laughed as Trump said: "Russia wants Ukraine to succeed."
What a profoundly stupid thing for the American president to say. Look at Vladimir Putin's actions. Listen to his words.
It's hard to know sometimes whether Trump is just ignorant, tuned out of the detail, or actually in Putin's pocket. Zelenskyy probably has a view but managed, just, to hold his decorum.
Beyond the spectacle of Zelenskyy's face, there were some other important moments - if only because they will act as markers when Trump shifts his position, as he has so many times.
On US security guarantees, Zelenskyy seemed reassured that Trump's America would provide some sort of military backdrop - to counter renewed Russian aggression in the future. But neither leader spelled out what that would look like.
Ukrainian sources have told me that Trump's commitment to back his support for Ukraine with security guarantees is a key point (never mind the fact that Trump did this months ago and then backtracked).
The same sources have also said that Trump's apparent willingness to go to Ukraine and address parliament there, which he articulated today for the first time, is a positive commitment.
Let's see if he sticks to it, or shifts again, and on the security guarantees.
The most articulate moment from the meandering and confused news conference came from Zelenskyy when he charted progress with percentages.
He said:
- "20-point peace plan, 90% agreed"
- "US-Ukraine security guarantees, 100% agreed"
- "US-Europe-Ukraine security guarantees, almost agreed"
So, that confirms Zelenskyy has accepted US commitments on security guarantees but shows that more work is required to pin down some elements in US-Europe security co-operation.
That's key because it involves the prospect of European troops on the ground in Ukraine. It's a Russian redline - and Trump knows that.
It's easy to get lost in all this: the progress, the positions, the multi-point plans and the spin.
But remember a few fundamentals. First, Trump may want this war to end, but he doesn't care how it happens. Second, Putin has shown no genuine signals that he wants the war to end. Third, Ukraine doesn't want to be forced into a subjugating surrender.
A few weeks ago the Americans produced a 28-point plan. It amounted to a Russian wish-list.
Since then, the Ukrainians, with the Europeans and co-ordinating with the Americans, have refined it. It's 20 points now, and within it are plenty of Ukrainian concessions.
Europe and Ukraine now expect Trump to focus the pressure back on Moscow and to engage Vladimir Putin in a way that moves him.
Don't hold your breath.
The historic tweets by Alaa Abd El-Fattah emerged after he returned to the UK on Boxing Day following several years of imprisonment in Egypt.
He has since apologised "unequivocally" for his "shocking and hurtful" past social media posts, in which he appears to call for violence against "Zionists" - but said some had been "completely twisted".
Politicians and government across the spectrum had campaigned for his release. On his return to the UK, Sir Keir said he was "delighted" the activist was "back in the UK".
Speaking to journalists this morning, the prime minister's spokesperson reiterated that Mr Abd El-Fattah case was worked on by successive governments before condemning his "abhorrent" tweets.
They added however that it does not "change the fact" that Mr Abd El-Fattah is a British citizen, and the apology was "right" and "unequivocal" - appearing to play down the likelihood of him having this status removed.
It is understood the Foreign, Commonwealth and Development Office is now looking at the processes around the activist's case.
Overnight, Mr Abd El-Fattah released a lengthy statement, in which he said: "I am shaken that, just as I am being reunited with my family for the first time in 12 years, several historic tweets of mine have been republished and used to question and attack my integrity and values, escalating to calls for the revocation of my citizenship."
He added: "Looking at the tweets now - the ones that were not completely twisted out of their meaning - I do understand how shocking and hurtful they are, and for that I unequivocally apologise."
Mr Abd El-Fattah was a leading voice in Egypt's 2011 Arab Spring uprising and went on hunger strikes behind bars.
He was most recently detained in September 2019 and sentenced to five years in prison in December 2021, on charges of spreading false news.
UN investigators branded his imprisonment a breach of international law, and both Conservative and Labour governments lobbied for his release.
Egyptian president Abdel-Fattah el-Sisi pardoned the activist earlier this year and he flew to the UK to reunite with his young son, who lives in Brighton, last week.
He had been granted UK citizenship in December 2021 under Boris Johnson, reportedly through his UK-born mother.
'I take allegations of antisemitism very seriously'
After the historic social media posts came to light, Conservative leader Kemi Badenoch, shadow justice secretary Robert Jenrick and Reform UK leader Nigel Farage called for the home secretary to look into whether the activist can be stripped of his UK citizenship and deported.
In his statement, the activist highlighted that he is now a middle-aged father, but said the posts were "mostly expressions of a young man's anger and frustrations in a time of regional crises" and the "rise of police brutality against Egyptian youth".
He continued: "I particularly regret some that were written as part of online insult battles with the total disregard for how they read to other people. I should have known better."
Mr Abd El-Fattah said he took allegations of antisemitism "very seriously" and that some of the tweets had been "misunderstood, seemingly in bad faith".
A tweet being shared to allege homophobia was actually ridiculing homophobia, he said, while another had been "wrongly interpreted to suggest Holocaust denial - but in fact the exchange shows that I was clearly mocking Holocaust denial".
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Mr Abd El-Fattah said he had been looking forward to celebrating his son's birthday with him for the first time since 2012, when he was just a year old.
He missed those birthdays because of his "consistent promotion of equality, justice and secular democracy", he said. This included "publicly rejecting anti-Jewish speech in Egypt, often at risk to myself, defence of LGBTQ rights, defence of Egyptian Christians, and campaigning against police torture and brutality - all at great risk".
Mr Abd El-Fattah said it had been "painful" to see some people who supported calls for his release now feeling regret.
"Whatever they feel now, they did the right thing," he continued. "Standing up for human rights and a citizen unjustly imprisoned is something honourable, and I will always be grateful for that solidarity."
He finished by saying he had "received huge empathy and solidarity from people across the UK, enough to win me my freedom, and I will be forever grateful for this".
A Foreign Office spokesperson said it had been a "long-standing priority under successive governments" to work for Mr Abd El-Fattah's release, "and to see him reunited with his family in the UK".
However, the government condemns the "abhorrent" historic tweets, the spokesperson added.
It is understood Prime Minister Keir Starmer was not aware of the social media posts when he celebrated Mr Abd El-Fattah's returned to the UK.
The father, a serving member of Gloucestershire Police, survived and was taken to Gloucestershire Royal Hospital for treatment.
The mother and two children, a seven-year-old girl and a four-year-old boy, were initially unaccounted for, but police have since confirmed their deaths.
Authorities said the fire is not suspicious and is a "tragic accident".
Emergency teams were called to a property on Brimscombe Hill, near Stroud, at around 3am on 26 December, a Gloucestershire Police spokesperson said.
Officers attended the scene alongside crews from Gloucestershire Fire and Rescue Service and the ambulance service.
The mother and father awoke around 3am and tried to get to their children, but were unable to due to the ferocity of the fire, DSI Ian Fletcher said in a briefing on Monday.
"The father has smashed his way out of the house through a bathroom window in order to try to access the children's bedroom via the outside."
However he was unable to get back into the property.
Mr Fletcher added: "We have multiple witnesses who describe the anguish that he was going through, his inability to get in and save his children and save his wife.
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Deputy Chief Fire Officer Nathaniel Hooton said firefighters worked extremely hard to get in as the fire raged in the house.
There is significant damage to the property internally, and work continues to try to find out what started the fire, he said.
Speaking near the scene, Reverend Peter Francis, the vicar of Holy Trinity Church, Brimscombe, told Sky News West of England and Wales correspondent Dan Whitehead: "It's an absolutely terrible tragedy. It's really shocking. It's impacted people so deeply.
"There are no words to express what has happened. Our thoughts and prayers are with the family and with all who are grieving at this time."
The man is thought to have been the driver of one of two vehicles involved in the collision on London Road at around 8.25pm on Sunday.
Norfolk Police said he left the scene holding what was described as a handgun and was shot by armed officers nearby.
The man, believed to be aged in his 60s, was pronounced dead at the scene.
The force has notified the police watchdog, the Independent Office for Police Conduct (IOPC), which has launched an investigation.
Assistant Chief Constable David Buckley said: "We understand this incident will cause concern in the community.
"Our highly trained armed officers deploy to hundreds of firearms related calls each year, but incidents where police discharge firearms are thankfully incredibly rare. A full and independent investigation is already underway.
"We are of course cooperating fully with the IOPC investigation and will be handing over all bodyworn footage and 999 calls to ensure transparency.
"We are not looking for anyone else in connection with the incident."
Police said the A11 remains closed in both directions from the Thetford Ranges roundabout to the Brandon Road roundabout.
The IOPC said it has begun an independent investigation.
The watchdog said in a statement: "At this early stage, we have established via police call logs that Norfolk Constabulary officers responded to a report of a collision involving two vehicles on London Road shortly before 8.30pm.
"Armed officers responded after it was reported that a man was seen leaving the collision scene holding what was described to be a handgun.
"Officers found a man by the A11 a short time later. We can confirm that two shots were fired by police shortly before 9pm.
"First aid was provided at the scene, however the man was sadly declared deceased shortly before 10.15pm."