An investigation is under way into the cause of the crash, government spokesman Lambert Mende said on Wednesday.
“Thirty-seven people have died, but the police fear that there will be more,” Mende told AFP.
He said it appeared that engine failure had caused the train to speed out of control near Kamina in the mineral-rich southern province of Katanga.
“The transport and health ministers are on their way to the site,” he added.
The DRC’s antiquated train network is currently undergoing a refurbishment programme paid for by the World Bank.
Train accidents are fairly common in the restive country, and there has been only scant investment in the system – which was originally built by Belgian colonisers – since the country gained independence in 1960.
In September 2012, four people were killed and another 37 injured after an accident north of the second largest city Lubumbashi.