Crowded passenger train goes off the tracks along the route that links capital Yaounde with economic hub Douala.

At least 70 people were killed and nearly 600 injured when an overloaded passenger train travelling between Cameroon’s two largest cities derailed and overturned.

“My heartfelt condolences to the bereaved families of the Camrail train derailment in Eseka. Over 70 passengers died and 600 wounded in the accident,” President Paul Biya, who is travelling abroad, wrote on his official Facebook page.

Transport Minister Edgar Alain Mebe Ngo’o said Friday’s accident took place near the central town of Eseka – 120km west of the capital Yaounde – as the train travelled to the economic hub of Douala.

“The cause of the accident is not yet clear,” said the minister, via state broadcaster CRTV, adding that several of the injured were in a very serious condition.

Rail officials said the train had been carrying 1,300 passengers, instead of the usual 600. The collapse of a bridge along the main highway between the capital and Douala had prompted more people to undertake the journey by rail.

Passenger Joel Bineli told Reuters news agency he saw three dismembered bodies on the tracks at the accident site.

Photos posted on social media purporting to have been taken at the scene showed several wagons overturned on a slope beside the tracks.

“There was a loud noise. I looked back and the wagons behind us left the rails and started rolling over and over. There was a lot of smoke,” said a Reuters journalist travelling on the train.

He added that prior to the train’s departure from Yaounde, a railway employee said eight additional wagons had been added to the normally nine-wagon train in order to accommodate extra passengers.

It remains unclear whether that played a role in the accident.

“Intervention and security teams have been mobilised,” the rail company Camrail said.

The route is one of the busiest in the country with trains to Chad and the Central African Republic also using the axis, which has a poor safety record.

In 2014, Cameroon began building its first highway between the two towns, but the work is not due to be completed until 2018.