A search operation is underway for 25 persons who remain unaccounted for after a ship with about 42 people on board capsized in the waters off Indonesia's South Sulawesi province, according to an official.

The vessel capsized at 1 p.m. in the Makassar Strait on May 26, but the incident was reported to the provincial search and rescue office on Saturday, the official told Xinhua news agency.

"After receiving the information, we immediately deployed our personnel and equipment to the scene for a search and rescue mission.

"About 45 rescuers and a ship have already been on the spot near a small island," the official said, adding that a plane or chopper will be dispatched to join the search.

So far, 17 people on board the ill-fated vessel have been rescued.

According to the official, the ship suffered an engine failure when it was hit by huge waves in the strait after departing from the Paotere Harbor in Makassar, the capital of the province.

The ship was heading to a seaport in Pangkajene district.