"The mishap happened when some five coaches of the superfast Rajdhani Express derailed in the state's Chapra district at 2:30 a. m. (local time). While four passengers were killed on the spot, those injured have been admitted to nearby hospitals," he said on condition of anonymity.
The train, which originated in the Indian capital, was going to the northeastern state of Assam when the mishap happened.
Local TV channels showed footage of rescuers trying to bring out those still trapped inside the derailed bogies.
A probe has been ordered into the incident, the official said, while ruling out any sabotage.