MANILA, Philippines (AP) — The Philippine coast guard said Saturday that seven people remain missing in a ferry sinking that killed two people in the country’s central region.

All 22 crew members and 39 of the passengers were rescued after the ferry sank early Friday in calm waters off Burias island, said Chief Petty Officer Bayani Belesario, deputy coast guard chief of Masbate province.

The cause of the sinking is under investigation, he said. Some passengers told local media the ferry tilted toward its front right side and quickly capsized more than halfway through its voyage from nearby Albay province.

The coast guard initially reported that 57 people, including 35 manifested passengers, were on board. Belesario said at least 70 are now known to have been on the ferry.

He said a search continues for seven missing passengers, including six who were not on the manifest.

Accidents at sea are common in the Philippine archipelago because of frequent storms, badly maintained boats and weak enforcement of safety regulations.

In 1987, the ferry Dona Paz sank after colliding with a fuel tanker in the Philippines, killing more than 4,341 people in the world’s worst peacetime maritime disaster.