Rescuers in Papua New Guinea have retrieved four bodies from the ferry that sank two days ago off the east Asian nation's coast.

Authorities said Saturday about 100 people are still missing.

Planes, ships and helicopters have been mobilized to search for survivors from the Rabaul Queen, which sank in rough weather Thursday with an estimated 350 people on board.

Nearly 250 passengers were rescued during a joint operation by Australian and Papua maritime crews. The operation was hampered by strong winds and large waves. The survivors were transported to Lae.

Rabaul Shipping, the owner of the vessel, say it is not clear what caused the ferry to sink.

Papua New Guinea Prime Minister Peter O'Neill has ordered an investigation into the disaster.