A constable with India's Railway Protection Force (RPF) has been arrested after he shot dead four people on a train near the city of Mumbai.

Authorities said the accused, Chetan Kumar, killed a senior RPF official and three passengers.

They said they are investigating his motive and trying to identify the dead passengers.

RPF personnel are tasked with the protection of railway passengers and property in India.

The shooting took place around 05:30 local time (midnight GMT) on a train travelling from Jaipur in the western state of Rajasthan towards Mumbai city in Maharashtra.

Mr Kumar first opened fire on Tikaram Meena, an assistant sub-inspector with the RPF, before shooting three other passengers, according to an RPF statement.

The incident occurred just after the train passed the town of Palghar, around 96km (60 miles) from the state capital, Mumbai. Mr Kumar then pulled the in-house alarm chain - used to stop trains in case of emergencies - and tried to escape, according to a statement from the Western Railways. He was arrested in the outskirts of Mumbai.

"The incident is very sad," Neeraj Verma, general manager of Western Railways, told reporters. "We have not received any information about any argument between the RPF constable and the assistant sub-inspector."