A Nigeria traffic compliance agency said on Tuesday that preliminary investigations showed the car involved in an accident in which former world heavyweight champion Anthony Joshua survived had a burst tyre before hitting a stationary truck.

The British boxer was in a "stable condition" in hospital after the Monday car accident that killed two close associates, his promoter said on Monday.

Joshua, 36, was admitted at Lagos's Duchess International Hospital, according to the Traffic Compliance and Enforcement Agency (Trace) in Ogun state where the accident occurred.

The smash happened on Monday morning on a main road linking Lagos and Ibadan in the south-west of the country.

Trace's spokesman Babatunde Akinbiyi said that "from the preliminary investigation that was conducted, definitely there was over-speeding on the part of the SUV Anthony Joshua was travelling in."

"In the course of that, the front tyre on the passenger side burst," he said. "That led to loss of control before the vehicle now swerved and rammed into the stationary truck that was parked. There was excessive speed...."

Pictures and videos circulating online and also shared by local state authorities showed a shirtless Joshua – a British national of Nigerian heritage – grimacing as he was helped out of the car.

Others showed the mangled wreckage of a black sports utility vehicle.

His promoter Matchroom said the boxer's "close friends and team members" Sina Ghami and Latif Ayodele were killed and Joshua himself was taken to hospital "for checks and treatment."

Nigerian police said the two victims died "at the scene."

Joshua's family hails from the south-west Nigerian city and he is known to visit there when he is in the country. (AFP)