At least six people have died and 129 remain missing as search and rescue operations entered their third day after an Indonesian passenger ferry capsized in rough seas in the Java Sea.

Indonesia's National Search and Rescue Agency (Basarnas) said rescue teams have so far saved 108 people from the Virgo Transport 8 ferry, which overturned in the early hours of Sunday due to severe weather conditions. Efforts are continuing by sea and air to locate the missing passengers.

Authorities said the vessel lost contact while sailing on its scheduled route from Surabaya in East Java to Banjarmasin in South Kalimantan after encountering heavy seas.

Basarnas said the ferry departed Surabaya on Saturday carrying a total of 243 people, including 30 crew members.

Putu Sudayana, head of the Banjarmasin Search and Rescue Office, said the rescued passengers were transferred to nearby vessels, while some were taken to a port in East Java.

As the operation entered its third day, around 1,100 rescue personnel, supported by 17 vessels and 10 aircraft and helicopters, continued searching the area. However, underwater search operations have been delayed because of rough seas, with waves reaching between 1.75 and 2.5 metres. Officials said divers would begin underwater operations once weather conditions improve.

Basarnas and the Indonesian Navy are preparing a subsea operation at the wreck site, located about 30 metres below the surface. The mission will involve specialist divers, remotely operated vehicles (ROVs), underwater drones and a multibeam echo sounder to locate and assess the overturned ferry.

Officials said the vessel is lying upside down in an unstable position, and options including righting and refloating the ferry are being considered.

Despite the difficult conditions, authorities said they remain hopeful that more survivors may still be found and vowed to continue the search until all those on board are accounted for.(ILKHA)