An overloaded ferry capsized off Indonesia’s Sulawesi island, killing at least 15 people and leaving 19 others missing, rescuers said Monday.

The boat was traveling from Lanto village in Buton Central regency in Southeast Sulawesi province to nearby Lagili village when it capsized just after midnight on Monday, local search and rescue agency head Muhammad Arafah said.

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The wooden boat was carrying 40 people but was designed for just 20.

Rescuers were searching Monday for 19 people who were still missing in rough seas, while 15 bodies had been recovered and six people were rescued, Arafah said.

Three inflatable boats, two fishing boats and six divers were deployed to search for the missing people, he added.

Thousands of residents had traveled to their villages to celebrate the regency's 9th anniversary on Sunday, and many people were transported by fishing or passenger boats.

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Television news showed footage of people on fishing boats retrieving bodies in the overnight darkness, and grieving relatives waiting for information at a port and a local hospital.

Indonesia is an archipelago with more than 17,000 islands, and ferries are a common form of transportation. With lax safety standards and problems with overcrowding, accidents occur frequently.

In 2018, an overcrowded ferry with about 200 people on board sank in a lake in North Sumatra province, killing 167 people.

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In one of the country’s worst recorded disasters, an overcrowded passenger ship sank in February 1999 with 332 people aboard. Only 20 people survived.