SYDNEY (AFP) - A Chinese vessel involved in the rescue of 52 passengers of a Russian ship stranded in Antarctica may have been caught in heavy ice.

Officials tasked with freeing the scientific expedition on the Akademik Shokalskiy, which has been stuck since Dec 24, succeeded in flying them out on Thursday in an on-off rescue operation.

A helicopter from Chinese icebreaker Xue Long used a makeshift landing pad next to the marooned ship and ferried the scientists, tourists and journalists to an Australian government supply vessel, the Aurora Australis.

But it emerged later on Friday that the Chinese ship, which has not moved much for several days, may itself be trapped by thick ice, the Australian Maritime Safety Authority (AMSA) said.

"Xue Long notified AMSA at 1pm AEDT (0200 GMT) this afternoon it has concerns about their ability to move through heavy ice in the area," it said.

"The Aurora Australis has been placed on standby by the Australian Maritime Safety Authority's Rescue Coordination Centre Australia to remain in open water in the area as a precautionary measure."

AMSA said the Chinese ship would attempt to manoeuvre through the ice when tidal conditions are most suitable during the early hours on Saturday, adding that there was no immediate danger to those onboard.

The rescue mission has been beset by extreme conditions from the start, with the Xue Long and Aurora Australis both unable to break through the ice to free the stranded Russian ship despite several attempts.

Rain, snow and wind had also delayed the helicopter flights to the vessel ice-bound 100 nautical miles east of the French base Dumont d'Urville.

"This one was quite difficult to do," said Mr John Young, general manager of the AMSA's emergency response division, of the rescue.

"All Antarctic operations are difficult just because of the nature of the place and in this particular case the movement of the ice and the changing of the weather introduced their own complications.

"The protracted nature of operations in Antarctica and the difficulty of getting good weather windows, and getting the right ice conditions, really make life very difficult."

Passengers on the stranded Russia ship were transferred to the Aurora Australis - the Australian Antarctic Division's supply ship - and had been heading slowly to Casey station.

They were transferred, using the Chinese icebreaker Xue Long's helicopter, from the Russian ship to an ice floe near the Aurora Australis over four flights across about 14 nautical miles on Thursday.

The complicated rescue has prompted questions about the cost of the mission and whether ships should be allowed into Commonwealth Bay, where the Russian vessel became trapped.

ASMA said the costs would broadly fall to the ships involved, and it would attempt to hold a briefing with all those involved in the rescue, but that any inquiry into the conduct of the Akademik Shokalskiy would have to be addressed by Russian authorities.

"Lessons learned from those processes may be fed into the International Maritime Organisation, and the guidelines and rules it creates for polar operations which is quite an active subject... at the moment," Mr Young said.

AMSA has said the Shokalskiy, which still has 22 crew onboard, would attempt to free herself when circumstances permitted.

"It's not an entirely risk-free environment for the ships as the ice moves," he said of the Shokalskiy and Xue Long earlier Friday.