Officials believe more than 100 people still missing after Thursday's ferry disaster off the coast of Papua New Guinea may be trapped inside the sunken vessel.

A spokesman for the Pacific nation's maritime safety agency says the Rabaul Queen quickly sank after it was hit by three strong waves while

traveling between the island of New Britain and the town of Lae.

The boat was believed to be carrying about 350 people at the time of the disaster, most of them students. Nearly 250 passengers were rescued by during a joint operation by Australian and Papua maritime crews, which was hampered by strong winds and large waves.

The survivors were transported to the city of Lae.

The search resumed Friday morning with three merchant ships backed by three Australian rescue aircraft.

Relatives angry over the lack of information from the ferry's operators threw stones at the company's offices in the town of Kimbe.

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