An overnight ferry packed with sleeping passengers capsized in heavy seas near the Pacific island of Tonga, leaving more than 30 people missing and two confirmed deaths.

Rescuers plucked more than 50 survivors from the water, but hopes were fading for the remainder after almost a full day of searching.

Australian Prime Minister Kevin Rudd, hosting a summit of South Pacific leaders, indicated the toll was expected to rise much higher.

He said: “There has been considerable loss of life. Our thoughts and our prayers are with the families of those that have been affected by this great tragedy.”

Many of those unaccounted for were women and children who may have been trapped below decks when the Princess Ashika overturned around midnight Wednesday, some 55 miles northeast of the capital, Nuku’alofa.

The ferry was on its way from Nuku’alofa to outlying islands in Tonga’s north. It sank in 115 feet of water in rough seas in a location that had made rescue efforts difficult.

Survivor Siaosi Lavaka told the Matangi Tonga news website that “No women or children made it. It appears that those passengers who were inside the vessel in cabin-type accommodation did not actually gain exit; only those who were outside.”

Most survivors were rescued from lifeboats soon after the search was launched early Thursday, and there were no sightings of other survivors afterward, said Mike Roberts, a spokesman for the New Zealand Rescue Coordination Center.

The ferry sank fast, “but we don’t know why,” said Neville Blackmore, a New Zealand rescue official.