Rescuers in Papua New Guinea are searching for more than 100 people still missing after a ferry sank off the coast of Papua New Guinea Thursday morning.

Officials say 238 survivors have been saved so far in a joint Australian-Papua rescue operation after the ferry Rabaul Queen sank. News reports from the region say about 350 people are believed to have been aboard, most of them students.

Papua New Guinea's Prime Minister Peter O'Neill said the cause of the accident is yet to be confirmed.

''We have the offices of the National Maritime and Safety Authority and Morobe Provincial Disaster office and our own National Disaster Office is now attending to this. We have now dispatched close to four vessels and a helicopter within the area so they can rescue the survivors and those who have been affected by this disaster. Again our sympathies to the families and the persons who have been affected by this disaster.”

Australia has also dispatched vessels and aircraft to help the rescue efforts. Prime Minister Julia Gillard called the accident a major tragedy.

“”There has been a boat go down in PNG (Papua New Guinea) with, as we understand it, 350 people on board. So, this is obviously a major tragedy. 350 people on board a ship that has gone down. We have been asked to provide assistance to PNG and we are providing assistance to PNG. We are also working to urgently ascertain whether or not there were any Australians on board. But given the likely very high loss of life here, I think, you know, when this news comes to the attention of Australians around the country, they will be thinking about the people of PNG as they respond to this tragedy.”

Earlier Thursday, Nerae Marimahu, a spokeswoman with the Pacific nation's National Maritime Safety Authority in Port Moresby, told VOA the MV Rabaul Queen sank about 16 kilometers off Cape Fortification. She said it was not immediately clear why the ferry sank.

The ferry's operator says it lost contact with the vessel as it was traveling between the island of New Britain and the town of Lae.