US ship on Antarctic ice break mission

ALL Antarctic rescue hopes rest on American icebreaker Polar Star, which has left Sydney on its mission to free two ships trapped by thick ice.

The US Coast Guard's Polar Star accepted a request from the Australian Maritime Safety Authority (AMSA) to help the Russian ship Akademik Shokalskiy, which has been marooned since Christmas Eve.

It will also aid the Chinese icebreaker Xue Long, which was involved in a dramatic helicopter rescue of the Shokalskiy's 52 passengers last Thursday before also becoming beset by ice.

AMSA confirmed the Polar Star, which was on its way from Seattle for an Antarctic mission, had diverted course and was on its way to help.

It will take about seven days for the icebreaker, with a crew of 140 people, to reach Commonwealth Bay after collecting supplies from Sydney today.

The AMSA spokeswoman said the Polar Star had greater capabilities than the Russian and Chinese vessels.

"It can break ice over six metres thick, while those vessels can break one-metre ice," she told AAP on Sunday.

"The idea is to break them out, but they will make a decision once they arrive on scene on the best way to do this." AMSA will be in regular contact with the US Coast Guard and the captain of the Polar Star during its journey to Antarctica.

Twenty-two crew remain on board the Shokalskiy, which sparked a rescue mission after a blizzard pushed sea ice around the ship and froze it in place on December 24.

The scientists, journalists and tourists on board the research ship were airlifted to safety last week, via the Xue Long's helicopter.

Those passengers are now on board Aurora Australis on their way to Australia's Antarctic base at Casey Station, and then Tasmania. The Aurora was forced to suspend its resupply of the Australian base to rush to the aid of the Shokalskiy, but it is not yet known what impact the incident will have on scientific program.

China has vowed "all-out efforts" to assist the Xue Long, which is surrounded by ice of up to four metres thick and is 21 kilometres from open water, according to state news agency Xinhua which has reporters on board.

"If the ship is stranded for a very long time, which is very rare indeed, then we'll have to evacuate the people on board and leave the vessel there," Chinese Arctic and Antarctic Administration director Qu Tanzhou said.

Chris Turney, leader of the Shokalskiy's expedition to retrace the steps of Antarctic explorer Douglas Mawson, defended the mission on Sunday.

"The science on the expedition was supported by a number of major research institutions including NOAA (US National Oceanic and Atmospheric Administration), the University of Wisconsin and a host of others," he said.

Turney said there was a long history of both governmental and private vessels going to the assistance of others in the Antarctic.

The Austrailian