The cause of the sinking is still being investigated, but some survivors told authorities the boat swayed suddenly and capsized after hitting a large log while sailing in strong winds, local police chief Norhayat, who goes by a single name, said.
Two tugboats and two inflatable boats have been searching for the missing people since Thursday night, battling high waves in the overnight darkness, said Norhayat, adding that a tugboat pulled the capsized boat to a port before dark on Thursday to ease the search efforts.
Boat tragedies are common in Indonesia, an archipelago of more than 17,000 islands, where ferries are often used as transport and safety regulations can lapse.
In 2018, an overcrowded ferry with about 200 people on board sank in a deep volcanic crater lake in North Sumatra Province, killing 167 people.
In one of the country’s worst recorded disasters, an overcrowded passenger ship sank in February 1999 with 332 people aboard. There were only 20 survivors.