The operators of a ship stricken in the southern ocean are facing a multimillion-dollar expense bill, as a third vessel began a rescue attempt five days after the tourist ship became trapped in sea ice.

A group of scientists, explorers and tourists aboard the Akademik Shokalskiy have been stuck about 1500 nautical miles south of Hobart since Christmas Eve. On Christmas Day, the Australian Maritime Safety Authority asked that the Aurora Australis and two other ships, a Chinese and a French ice-breaker, sail to assist the trapped ship.

The Aurora, an Australian-flagged vessel, cut short its mission to resupply the Casey station in Antarctica for the year ahead, and was due to reach the area about midnight on Sunday.

The two smaller ice-breakers had earlier been unable to break through the ice.

Under the Treaty of the Safety of Life at Sea, vessels are required to respond to a distress message, with the costs incurred a matter for the ship owners after the event, the AMSA said.

These can include fuel costs, crew costs and loss of revenue.

Dr Rob Massom, an expert in sea ice at the Australian Antarctic Division and Climate Change and Ecosystems Co-operative Research Centre, said it was not unknown for sea ice to form into tightly packed ice very quickly.

''Although it's summertime, the ice can blow around, causing ships to get penned in the ice,'' he said.

Sea ice packs can also raft up on top of each other, doubling the thickness of the ice and forming pressure ridges several metres thick, he said.

Summer was the safest time for tourist ships to go to Antarctica but there were always risks, he said.

Nicky Phillips and Colin Cosier are travelling on board the Aurora Australis as part of the Australian Antarctic Division's media program.