The passengers, mostly Hindu pilgrims, had just alighted from a local train at Dhamara Ghat station and were on their way to a temple in Saharsa district.
An angry crowd is said to have beaten the driver and set two coaches on fire.
Rescue operations are under way and police reinforcements have been sent.
Senior state police officer SK Bhardwaj said it was difficult to say how many people had died as many bodies had been dismembered.
The incident took place at 08:40 India time. The pilgrims were hit by the Rajya Rani Express travelling on the opposite track.
Life does not always give an opportunity to celebrate . There are sad moments on life also that one needs to cope up with. May their souls rest in peace.