Fifty others were trapped inside the goods train after 12 of its carriages flipped off the track in the accident near Likasi, a mining town between Lubumbashi and Kolwezi in the copper and cobalt-rich southeast.
"Evidently the train was going too fast, the driver came to a curve and had to break suddenly leading to the accident," said Dikanga Kazadi, Katanga's interior minister.
He said the priority was rescuing those still trapped and a team had been sent to investigate the cause of the accident. A witness said he counted 37 bodies at the scene.
"There were two train engines and two carriages overturned," he told Reuters, asking not to be named.
Congo's infrastructure is in tatters after decades of neglect and conflict so people struggle to travel around the vast nation, which is roughly the size of Western Europe.
More than 100 people were killed in a 2007 accident involving people travelling onboard a goods train in the province of Kasai Occidential.