Papua New Guinean authorities Saturday began retrieving the bodies of those killed when a crowded ferry sank two days ago in what is thought to be among the nation's worst sea accidents.

More than 100 people are still missing from the MV Rabaul Queen, which went down about nine nautical miles off the coast early Thursday. Air and sea search efforts were ongoing despite rough weather.

"Four bodies were picked up from the water," rescue coordinator Captain Nurur Rahman from PNG's National Maritime Safety Authority told AFP.

"The water at this time is still rough which is slowing down a little bit the search and rescue. We haven't found any survivors today."

Rahman said the bodies were discovered, along with debris from the wreck, about 50 nautical miles southeast of where the vessel sank.

The authority said the 246 people rescued in a joint rescue operation with neighbouring Australia were undergoing medical assessment at the Angau Memorial Hospital in Lae, a major coastal gateway and the doomed boat's destination.

As the search effort involving seven fixed wing aircraft, three helicopters and seven boats continued, some families in Lae were still hoping to find their loved ones among the survivors.

"I am still... waiting for them to arrive," one elderly woman told the Australian Broadcasting Corporation. "Maybe they are dead by now."

PNG-based Rabaul Shipping, the owner of the vessel, said Saturday it appeared that the boat had been hit by a freak wave which then left it vulnerable as another large wave came rolling in.

In a statement, it said it had spoken with the Rabaul Queen captain who had indicated weather conditions during the voyage were no worse than on some other journeys on the route.

"There were however large swells, prompting the captain to shift from an auto-pilot function and take manual control," it said.

"A freak wave hit the ferry, causing steering and positioning difficulties.

"A second large wave then hit the ferry as it was (in) a state of vulnerability, rolling it and causing it to sink in just minutes."

A second captain who was in the wheel house of the Japanese-built single engine ferry at the time has not been found, the company said.

The boat, which was travelling between Kimbe and Lae when it went down, had 351 passengers and 12 crew onboard, the firm said. Rahman said the boat was licensed to carry 310.

Rahman said officials had been unable to obtain an official manifest for the voyage because the offices of the company involved had been in "lock down" since the accident as the relatives of those onboard gathered outside.

But Rabaul Shipping said it had handed the ferry manifest to local authorities within hours of the accident and was working to assist rescue efforts as best it could.

"We again express our deepest sorrow and condolences to the many people who are suffering because of this terrible tragedy," managing director Peter Sharp said in the statement.

PNG Prime Minister Peter O'Neill has ordered an immediate investigation into the tragedy while Queen Elizabeth II, the country's head of state, has sent a message of sympathy from Buckingham Palace.

Rahman said the accident was probably the worst sea tragedy to hit PNG.

"We do not know how many survivors we should be getting, but if we calculate it from today as it stands, then it is by far the worst one in history," he told AFP.

Source: AFP