Image caption The ship is being used by the Australasian Antarctic Expedition

A rescue mission for a ship trapped in ice in Antarctica is under threat as reports have emerged that one of the assisting vessels may itself be stuck.

Fifty-two passengers and four crew members were due to be evacuated by helicopter from China's Xue Long ship as soon as conditions allowed.

However, the Xue Long has barely moved in a day and may be stuck in the ice.

The research vessel Akademik Shokalskiy has been trapped for nearly a week with 74 scientists, tourists and crew.

The ship is stocked with food and is in no danger, the team on board says.

Media playback is unsupported on your device Media caption The BBC's Andrew Luck-Baker says confusion surrounds the fate of the rescue vessel

The planned air evacuation required that the two icebreakers in the immediate area - the Xue Long and the Australian Aurora Australis - be positioned close to each other in open water, clear of the pack ice.

However, the captain of the Xue Long has told the Shokalskiy that he is keeping his vessel in a "holding position".

The Aurora Australis, is now understood to be planning to carve through the dense thick pack to assist the Xue Long.

The initial plan had been for a helicopter from the Xue Long to carry people in groups of 15 up from the pack ice next to the Shokalskiy.

The airlifted passengers would then be transferred by a small boat, deployed from the Australian icebreaker, onto the Aurora Australis.

The expedition members would then have travelled to Australia's Antarctic base at Casey some four days' voyage away.

The Return to Mawson's Antarctica The 2013 Australasian Antarctic Expedition repeats scientific investigations made by Douglas Mawson and his team between 1911 and 1914

Andrew Luck-Baker and Alok Jha are reporting on the expedition for Discovery on the BBC World Service

Listen to Part One, Part Two and Part Three of their story, or get the Discovery podcast

However, if the Chinese vessel is also stuck and the Australian vessel cannot help it reach clear water, there will be no airlift.

Under the initial plan, the remaining crew members would have stayed on board until another, more powerful US icebreaker arrived in up to 10 days' time, the BBC's Andrew Luck-Baker reports from on board the Akademik Shokalskiy

However, it may now be that all of those on board may have to wait for the US icebreaker, the Polar Star, he adds.

Earlier attempts by Chinese and French icebreakers to reach the ship were also foiled by the thick ice.

The Shokalskiy was trapped on Christmas Eve by thick sheets of ice, driven by strong winds, about 1,500 nautical miles south of Hobart - the capital of the Australian state of Tasmania.