BANJARMASIN, Indonesia — Indonesian authorities intensified a search Monday for 129 people who were missing after a ferry overturned in bad weather in the Java Sea on Sunday, killing at least six passengers.

The Virgo Transport 8 was carrying more than 240 people when its captain issued a distress call, saying the ship was listing in rough seas with waves of up to 3 meters (10 feet) while traveling from Surabaya in East Java province to Banjarmasin in South Kalimantan province, on Borneo Island.

Contact was lost with the ferry at about 2 a.m. Sunday and about two hours later authorities received information that the vessel had overturned in the Java Sea’s Masalembo waters, about 148 kilometers (92 miles) from Banjarmasin.

Videos released by the National Search and Rescue Agency on Sunday showed an overturned ferry floating in choppy waters during a helicopter search operation.

On Monday, 17 ships and aircraft were deployed for the search carrying about 655 personnel deployed from the military, police and other agencies, said Mohammad Syafii, the National Search and Rescue Agency chief.

Authorities were also deploying specialized underwater teams and navy-operated underwater thermal drones to strengthen search efforts and speed up the evacuation of victims, he said.

“We remain hopeful of finding more survivors,” Syafii told a video briefing.

Search teams, assisted by nearby tugboats and other passing vessels, rescued 108 people and recovered six bodies on Sunday.

The manifest said the ship carried 243 people including 213 passengers and 30 crew members, although it is common in Indonesia for the number of passengers to differ from the manifest. The 119-meter (390-foot) ferry, which was built in Japan in 1987, also was transporting 89 vehicles.

Authorities have not determined the cause of the accident.

A survivor, Ahmad Saudi, said the ferry appeared overcrowded, with many passengers forced to sleep in hallways and common areas because the cabins were full.

Saudi, a bus driver traveling with a vehicle he was transporting, recalled how the ferry suddenly listed without warning, triggering panic among passengers as rough seas battered the vessel in the Java Sea.

Passengers initially tried to hold on before scrambling to the higher side of the ship as it tilted further, he said, speculating the ferry’s balance may have been affected by trucks loaded on one side.

“The women staying in the economy-class cabins likely didn’t survive because the ferry listed so quickly,” Saudi said. “There were no alarms or announcements warning passengers about what was happening, many people in the cabins may not have had enough time to get out.”

Faisal, another survivor who goes by one name, said he and 14 other passengers clung to a section of the overturned ferry that remained above water after it capsized.

“After the ship listed, people panicked and rushed to the upper deck, but eventually the ferry rolled over completely,” he said. “Fourteen of us were left stranded there.”

The group repeatedly recited the Islamic call to prayer, or adhan, while battling exhaustion and rough seas as awaiting rescue. A wave later swept Faisal toward a lifeboat, helping him survive, he said.

Indonesia is an archipelago of more than 17,000 islands. Ferries are a common method of travel and accidents occur regularly, in part due to weak enforcement of safety standards.