Dozens of people are missing after a ferry sank off Indonesia's tourist island of Bali, rescuers said.

The boat was carrying 53 passengers and 12 crew members when it sank at 23:20 local time (15:35 GMT) on Wednesday while on its way to Bali from Banyuwangi on the eastern coast of Java island, the Surabaya office of the National Search and Rescue Agency said.

Four passengers were found on a lifeboat in the early hours of Thursday, while the search for more survivors continues.

Photos published by the Antara news agency showed ambulances on standby and residents waiting for updates by the roadside.

Authorities are investigating the cause of the sinking.

The ferry operator told local media that the vessel had reported engine trouble shortly before it sank.

Marine accidents are frequent in Indonesia, a sprawling archipelago of around 17,000 islands, where uneven enforcement of safety regulations is a longstanding concern.