Two fishermen have survived for almost a month in shark-infested waters off Australia, by floating in a large icebox after their boat sank.

The men, both from Burma and in their 20s, were on a 12-metre Thai wooden fishing boat with 18 others when it sank in stormy seas off Australia's north coast two days before Christmas.

"They had no safety equipment, no beacons, no means of communication and they'd been drifting for 25 days," said Tracey Jiggins of Australia's Maritime Safety Authority. "For them to have even been spotted in a huge body of water is amazing."

The men's desk-sized container was noticed by an Australian coastal patrol aircraft on Saturday. A photograph taken from the plane showed them standing in a high, red-sided icebox of the type used by commercial fishing boats to store their catch. The pair were waving desperately at rescuers.

The two fishermen were winched on to a rescue helicopter and taken to hospital on Thursday Island, off Australia's north coast. "They were desperately keen to get on. When they got up they skolled [drank] two litres of water each within seconds," the helicopter pilot, Terry Gadenne, told Australian television.

They were hungry and dehydrated after drifting for 25 days during the monsoon season, but were recovering well and would be released later today, hospital officials said.

The pair will be questioned by immigration officials and police. The Maritime Safety Authority said the rest of the crew would almost certainly have perished. No further search for survivors is planned.

"The information they provided to us was that they witnessed other crew members in the water, none of whom had any flotation device, so we've done an assessment and we don't believe anybody would be able to survive 25 days actually in the water," said Jiggins.

It was unclear where the Thai-registered fishing boat, crewed by Thais and a handful of people from Burma, sank. The surviving fishermen may have drifted for hundreds of miles before being picked up 60 nautical miles north-west of Horn Island.

The Torres Strait, between Australia and Papua New Guinea, is infested with sharks and the area is regularly fished by both licensed and illegal fishing vessels, many from Asia.