Six people were killed on Thursday when a train ploughed into a bus in Nigeria's commercial capital Lagos, the emergency services said.

The accident, which happened in the PWD area of a city of more than 20 million, also seriously injured dozens.

The Lagos State Emergency Rescue Agency (LASEMA) said the bus driver apparently tried to beat a warning signal before the approaching train slammed into the vehicle.

"The death toll is now six -- four females and two males," Ibrahim Farinloye of the National Emergency Management Agency (NEMA) told AFP, revising an initial toll of two.

He said 74 people were injured, with some critically.

"The death toll might rise further because a lot of people are in critical condition in the hospital," he said.

Farinloye said emergency workers struggled for hours before they could rescue people trapped in the wreckage of the bus, which was left mangled at the front of the train.

The train had been travelling from Ijoko in nearby Ogun state and heading to the Ebute-Meta area in Lagos.

LASEMA blamed the bus driver's "reckless driving," accusing the driver of trying to scoot across the line in defiance of a signal warning of an approaching train.

The agency said in a statement the wreckage of the bus and the train had been removed.

Accidents are common on Nigeria's poorly maintained roads as a result of speeding, reckless driving and disregarding traffic rules.