PORT MORESBY - Rescuers battling big waves and strong winds have pulled nearly 250 people from the sea off Papua New Guinea's east coast after a ferry sank. More than 110 people remained missing Friday.

Crews in ships, planes and helicopters continued to scour the warm seas. Papua New Guinea's National Maritime Safety Authority rescue co-ordinator Capt. Nurur Rahman said he had not given up hope of finding more survivors, though the swell and winds were rising and some victims may have been trapped inside the sunken ferry.

"I do not presume them to be dead yet," he told Australian Broadcasting Corp.

Owners of MV Rabaul Queen, Papua New Guinea-based Rabaul Shipping Company, said Friday there had been 350 passengers and 12 crew aboard the 22-year-old Japanese-built ferry when it went down Thursday morning while travelling from Kimbe on the island of New Britain to the coastal city of Lae on the main island. A police official said most of those aboard were students.

"We are stunned and utterly devastated by what has happened," managing director Peter Sharp said in a statement.

The company said the cause of the disaster remained unclear, but National Weather Service chief Sam Maiha told Papua New Guinea's Post-Courier newspaper that shipping agencies had been warned to keep ships moored this week because of strong winds.

An official at the scene told the newspaper that the ferry capsized in rough seas and sank four hours later.

By nightfall Thursday, 246 survivors had been rescued by merchant ships battling 16-foot (5-meter) swells and 45 mph (75 kph) winds at the disaster scene 50 miles (80 kilometres) east of Lae and 10 miles (16 kilometres) from shore, the Australian Maritime Safety Authority said.

AMSA spokeswoman Carly Lusk on Friday could not explain why the new figure was eight greater than the tally of 238 survivors released by her agency late Thursday.

Capt. Rahman said the sea temperature was above 68 degrees Fahrenheit (20 degrees Celsius) -- warm enough for people to survive for an extended period.

"Because of the proximity of the shore, ... I still have high hopes to have many more survivors," he said.

He said the ferry sank in 3,300-foot (one-kilometre) deep water, making it difficult to determine whether bodies were trapped inside.

The survivors were delivered to Lae, the South Pacific country's second-largest city, by five ships early Friday, said the AMSA, which is assisting Papua New Guinea authorities with the rescue.

"None of them had sustained any real injuries. They were pretty cold and miserable," Lae Chamber of Commerce president Alan McLay told Sky News television.

The search continued at first light Friday with three ships, two airplanes and two helicopters, AMSA said.

An angry crowd threw stones at the Kimbe office of Rabaul Shipping Company on Thursday night, outraged at a lack of information, police said.

"There were a lot of people crying and then they wanted to know the fate of their loved ones, the people actually who were on board," Kimbe Police Inspector Samson Siguyaru told ABC.

"I had to send in the police to rescue (staff and), get them out of the office to a location where it is safe," he added.

Siguyaru said the passengers were mostly students returning to school at Lae.

The company said the ferry's captain had made routine radio contact with another vessel before sinking and gave no indication anything was wrong.

Papua New Guinea Prime Minister Peter O'Neill said the cause of the accident was unknown, but acknowledged that safety in the shipping industry was lax.

"We need to bring some safety measures back into this industry," O'Neill told reporters.

Australia's High Commissioner to Papua New Guinea, Ian Kemish, said bad weather played a part.

"I think it's a fair bet that the very severe weather that's being experienced in some parts of Papua New Guinea played a role, but I can't say much more about the cause of the sinking beyond that at this stage," he told ABC.