A US icebreaker was dispatched yesterday to assist an icebound Russian research ship and Chinese vessel trapped during a rescue bid in the Antarctic.

The Polar Star accepted an Australian request to go to the aid of the marooned Russian ship Akademik Shokalskiy which has been beset by ice since December 24.

It will also aid the Chinese icebreaker Xuelong, or Snow Dragon, which was involved in a dramatic helicopter rescue of the Shokalskiy's 52 passengers last Thursday.

The Snow Dragon has itself become trapped, with China vowing "all-out efforts" to assist the ship which is surrounded by ice of up to 4 meters thick and is stuck 21 kilometers from open water, Xinhua news agency said.

Authorities say the 101 crew aboard the Chinese ship and 22 aboard the Russian ship were well provisioned and in no immediate danger.

China's Antarctic division director Qu Tanzhou said the Snow Dragon may attempt to chop itself free of the ice today if conditions permit.

"Weather forecasts and ice monitoring show favorable weather conditions may appear on Monday, which may bring winds to blow the ice floe away, providing a good opportunity for Xuelong to sail out," Qu said yesterday.

Scientists aboard the Snow Dragon were continuing their research even as the vessel lay stranded.

Gao Jinyao, from China's State Oceanic Administration, said they were collecting data from a geomagnetometer he had set up on the vessel, as the area where it is stuck is close to the South Pole.

"The data will be first-hand material when we study submarine tectonics and build the earth's geomagnetic field model," Gao said.

Other members of the team were observing ice flow and sampling the air.

The icebreaker has also created a one kilometer "ice-breaking runaway," waiting for favorable weather conditions, Xinhua said.

Polar Star leaves Sydney

The Polar Star, which left the US in early December to clear a channel for ships resupplying McMurdo Station research base, left Sydney yesterday with provisions, according to the Australian Maritime Safety Authority.

The 122-meter ship is capable of continuously breaking ice up to 1.8 meters thick while travelling at three knots, and can break ice more than six meters thick by ramming. It is expected to take seven days to reach Commonwealth Bay where the two ships are trapped.

The stranding of the Shokalskiy, which was carrying 22 scientists, 26 paying passengers and four journalists as well as 22 crew who remain on board, has sparked criticism in some quarters.

As well as the Snow Dragon and Polar Star, two other icebreakers, Australia's Aurora Australis and France's Astrolabe, were diverted from their Antarctic missions to assist the Shokalskiy.

Yves Frenot, director of the French Polar Institute, said the rescue saga had forced French scientists to scrap a two-week oceanographic campaign.

He said his counterpart in Australia was "spitting tacks" because their entire summer has been wiped out, he said.

The Australis was forced to suspend its resupply of the Australian base to aid the Shokalskiy, but authorities said it was not known what impact there would be on scientific programs.

Chris Turney, leader of the Shokalskiy's expedition which repeated century-old measurements to explore environmental changes as it retraced a 1911-14 voyage, hit back at Frenot.

"Yves was fully aware of the expedition and there was even an exchange of emails around it in September. At no time did Yves indicate any problems with the science of the expedition or the expedition itself," Turney said.

He said there was a long history of government and private vessels going to the assistance of others in the Antarctic.