A US Coast Guard heavy icebreaker has left for Antarctica in an attempt to rescue more than 120 crew members aboard two icebreakers trapped in pack ice near the frozen continent's eastern edge, officials said.

The 122-meter (399-foot) cutter, the Polar Star, left Australia on Sunday in the wake of a Jan 3 request from Sydney, Moscow and Hong Kong to assist the Russian and Chinese ships because "there is sufficient concern that the vessels may not be able to free themselves from the ice," the Coast Guard said in a statement.

The Russian research ship Akademik Shokalskiy has been trapped in ice-clogged Commonwealth Bay since Christmas Eve, while the Chinese ship which came to its rescue, Xue Long or Snow Dragon in Chinese, reported on Friday it too had become stuck nearby.

A day earlier, the Chinese ship's helicopter had retrieved from the Russian ship 52 scientists, journalists and tourists who are now on their way home aboard an Australian icebreaker, Aurora Australis.

Authorities say the 101 crew aboard the Chinese ship and 22 aboard the Russian ship were well provisioned and in no immediate danger.

The Polar Star cut short its planned stop in Sydney, Australia, to assist. It left Sydney on Sunday morning local time, Coast Guard spokeswoman Chief Warrant Officer Allyson Conroy said in an email.

"Our highest priority is safety of life at sea, which is why we are assisting in breaking a navigational path for both of these vessels." Vice Adm Paul F Zukunft, the Coast Guard Pacific Area commander, said in a statement.

"We are always ready and duty bound to render assistance in one of the most remote and harsh environments on the face of the globe."

The Australian Maritime Safety Authority's Rescue Coordination Centre, which oversaw the rescue, said the Polar Star, the Coast Guard's only active heavy polar icebreaker, would take about seven days to reach Commonwealth Bay, depending on weather.

Source: AP