Police officials say several carriages of the passenger train packed with sleeping travelers derailed and fell onto the path of a freight train near a small town in West Bengal state. Some of the carriages were badly crushed.
The passenger train was traveling from Kolkata in West Bengal state to Mumbai.
Officials say the number of casualties is could rise as rescuers struggle to reach a large number of passengers trapped in the mangled carriages. Survivors described scenes of chaos. Helicopters were used to evacuate the injured.
The head of police in West Bengal state, Bhupinder Singh, called it a clear case of sabotage.
Singh said Maoist rebels were to blame for the derailment. He says police found Maoist leaflets at the site.
The area where the crash occurred is a stronghold of Maoist rebels. The rebels, who say they are fighting for the rights of the poor and the landless, have stepped up attacks in recent months.