Two trains have collided in Indonesia's main island of Java, leaving at least four people dead and more than 20 injured.

Indonesian police and the railway operator said the accident took place near Bandung shortly after 6 a.m. on Friday local time.

A long-distance train and a commuter train collided, leaving several carriages overturned or badly damaged. The trains reportedly carried about 480 people.

The four victims were said to include crew members, while 22 people were being treated for their injuries.

Police and rescue personnel are combing through the wreckage, as there are reports that some people remain trapped between the carriages.

Indonesian authorities are investigating the cause of the accident.

Railways are a key means of transport for Indonesia's population of about 270 million, but they have been prone to accidents.

Japanese railway engineers are helping the country train maintenance and inspection workers to improve safety.