The U.N.-funded Radio Okapi said 30 to 40 people were believed dead in the accident, in which a number of cars flipped over in the Central African country's Kasai Occidental province - between the city of Ilebo and the provincial capital of Kananga.
Officials could not be immediately reached for further information.
Radio Okapi said the accident appeared to have been caused by a technical problem, but did not provide details.
Roads and rail are notoriously dilapidated in vast Congo - a country the size of Western Europe only starting to emerge from decades of war and corrupt dictatorship.
Brenton Tarrant, the shooter from New Zealand's Christchurch, was not a lone wolf. The West has missed out an important point - the formation of organised Christian extremism
Those who convientenly blame Muslims and Islam for "extremism" and "terrorism" should rethink and read the living history for truth, honesty and justice
The Moroccan occupation remains the last case of decolonization in Africa. The Moroccan military invaded in 1975 despite a clear ruling issued by the ICJ.