At least four people were killed and 80 were left injured after an express train derailed in India's northeastern state of Bihar, according to authorities on Thursday.

"Four casualties have been confirmed and a rescue operation is underway. Twenty-one coaches have derailed," Tarun Prakash, general manager of the East Central Railway, told the Times of India.

The train departed from the Anand Vihar Terminal railway station in Delhi and was bound for the Kamakhya Junction in Assam.

Cause unknown

The cause behind the derailment of the train was not immediately known.

Some of the injured people were sent to hospitals in Bihar's capital city, Patna, for treatment. 

Several passenger and goods trains have been diverted. 

Railways minister Ashwini Vaishnaw expressed his condolences on X, formerly Twitter, and pledged to find the cause of the derailment.

He also said an evacuation and rescue operation was "complete" and that passengers were shifted to a different train for their onward journey.

India has one of the world's largest railway networks and has seen several accidents over the years. In June, India witnessed its worst train crash in two decades when a triple-train collision in Odisha resulted in the death of at least 288 people.

mfi/jsi (AFP, Reuters)