An Antarctic ice shelf used as a runway is breaking away forcing an emergency airlift to close summer operations on the continent.

The situation is being complicated by the Christchurch quake which is limiting operations at Christchurch Airport.

Staff at New Zealand's Scott Base and the US's McMurdo Sound are scrambling to get people off Antarctica to Auckland.

With winter closing in, the prospect is that people either get out now or stay all winter.

CEO Lou Sanson told Radio New Zealand two giant US Air Force Globemasters are heading down tonight from Christchurch and will bring back several hundred Americans tomorrow.

They will be flown on to Auckland by the RNZAF.

But Sanson said they have a complication now that the Ross Ice Shelf is separating quickly from Ross Island where Scott Base and McMurdo are.

"We are seeing the biggest ever break out of the Ross Ice Shelf in 15 years, our supply lines to the airfield are getting affected."

Scott Base manager Troy Beaumont told Stuff this afternoon that the sea was opening up and access to the iceshelf was becoming difficult.

"The ice is breaking up," he said.

He said it was likely the Globemasters would be able to land at this point, but it would take staff longer to get onto the ice.

Scott Base is already in its winter operations, with only one New Zealander due out, but there are several hundred Americans needing to get out.

- © Fairfax NZ News