Nigerian President Muhammadu Buhari said 23 people, including students, were killed when a truck carrying petrol overturned and caught fire on Wednesday on a busy road in the centre of the country.

The presidency figure more than doubled an earlier toll of nine counted by an AFP journalist who visited the mortuary in Lokoja, the capital of Kogi state where the accident occurred.

"The death of 23 people as confirmed by the Federal Road Safety Commission, represents another disturbing and saddening incident in the litany of tragedies that have befallen our country," President Buhari said in a statement.

"I am seriously worried about the frequency of these unfortunate and large scale tragedies in the country which cause needless deaths," he said.

Fuel truck accidents happen frequently on Nigeria's ill-maintained roads.

The Nigerian leader urged road users to  comply with safety measures in order to prevent such tragedies in future.

Earlier the AFP journalist said he had counted nine bodies in the mortuary while several others suffered severe burns.

He said many vehicles, including a bus carrying students from the state polytechnic, were burnt in the inferno.

"The driver was coming from Okene and heading towards the northern part of the country when the brake of the truck failed on the Lokoja-Abuja highway," he said.

He said the truck then skidded off the road and caught fire.

The state's governor Yahaya Bello sent his condolences to the victims' families.

"It is very sad to learn of the tragic loss of lives, many vehicles, property and other valuables in the petrol tanker fire," Bello said in a statement.

He also offered his sympathies to the students at the polytechnic "over the death of some of their colleagues".