PORT MORESBY, Papua New Guinea (AP) — Rescuers plucked more than 230 survivors from the sea off Papua New Guinea’s east coast after a ferry sank Thursday with as many as 350 people on board, officials said.

An airplane from Australia, three helicopters and eight ships scoured the area after the MV Rabaul Queen went down while traveling from Kimbe on the island of New Britain to the coastal city of Lae on the main island, the Australian Maritime Safety Authority said.

The ferry sank 50 miles (80 kilometers) east of Lae, the South Pacific country’s second-largest city, and 10 miles (16 kilometers) from shore, it said in a statement.

Australian Broadcasting Corp. quoted police in Kimbe as saying that most of the passengers were students and trainee teachers.

An official at the scene said the ferry capsized in rough seas and sank four hours later, Papua New Guinea’s Post-Courier newspaper reported.

National Weather Service chief Sam Maiha said shipping agencies had been warned to keep ships moored this week because of strong winds, the newspaper said.

Papua New Guinea Prime Minister Peter O’Neill said the cause of the accident was unknown, but acknowledged that safety in the shipping industry was lax.

“We need to bring some safety measures back into this industry,” O’Neill told reporters.