An operation has begun in Antarctica to rescue passengers from the ice-bound research vessel Akademik Shokalskiy.

A Chinese helicopter arrived close to the vessel, bringing in a crew to assess the landing situation.

The aircraft is expected to return soon to begin ferrying the first passengers out to another vessel.

The Shokalskiy has been trapped since Christmas Eve. Its 22 crew are expected to remain on board once the 52 scientists and tourists have left.

The Shokalskiy was trapped 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.

The vessel is being used by the Australasian Antarctic Expedition to follow the route explorer Douglas Mawson travelled a century ago.

Weight restrictions

"The Chinese helicopter has arrived at the Shokalskiy. It's 100% we're off! A huge thanks to all," expedition leader Chris Turney tweeted.

Mr Turney's post showed a video of a red helicopter touching down on a site that had been marked out by the Akademik's crew.

Members of the crew checked the site and the helicopter took off again.

"If it all goes well we'll be off in about an hour's time," Mr Turney says in the video.

The Australian Maritime Safety Authority's Rescue Coordination Centre (RCC), which is overseeing the operation, had earlier said it was unlikely the airlift would go ahead on Thursday as hoped because of the sea-ice conditions.

The rescue involves ferrying groups of passengers by helicopter to the Chinese icebreaker Xue Long, from where they will be taken by sea to the Australian icebreaker Aurora Australis.

The passengers are not expected back in Tasmania until mid-January.

Despite being trapped, the scientists have continued their experiments, measuring temperature and salinity through cracks in the surrounding ice.