A gate man was injured in the mishap and rail traffic was briefly disrupted on the Delhi-Howrah rail line, police said.
The mishap took place this morning when a bus was crossing the track and developed some technical problem.
The gate man was trying to push the vehicle from the track when the Gorakhdaham Express hit the bus and dragged it over a hundred meters.
The engine of the train derailed due to the impact of the collision. There were no passengers in the bus and the driver had managed to jump to safety.