The Coast Guard said in a release the Polar Star was responding to a Friday request from the Australian Maritime Safety Authority to assist the Russian-flagged cruise ship Akademik Shokalskiy and the Chinese-flagged icebreaker Xuelong. The Coast Guard said the Russian and Chinese governments also requested U.S. assistance.
The Chinese icebreaker had been deployed to evacuate passengers from the trapped Russian ship only to find itself stuck in icy seas itself, Chinese officials said.
The captain of the Xuelong said high tides around Antarctica were creating dicey conditions that pushed a huge iceberg and other large floes into the vessel's area.
Skipper Wang Jianzhong told China's official Xinhua News Agency he would get under way once the iceberg drifted out of the area.
A helicopter from the Xeulong, which means Snow Dragon, transported 52 passengers this week from the icebound Akademik Shokalskiy to the Australian vessel Aurora Australias.
The Australian Maritime Safety Authority said the Xeulong was not in any immediate danger. The agency had ordered the Aurora Australias to remain in open water for the time being in case its assistance is needed, but gave it the green light Saturday to continue on its course, the BBC said.
The Aurora Australias and the passengers from the Akademik Shokalskiy were scheduled to make a supply run to an antarctic base before returning to port in Tasmania.
The 22 crew members of the Akademik Shokalskiy remained stuck in the ice Saturday, waiting for warmer temperatures that would allow it to free itself from the heavy pack ice, Russia's RIA Novosti news agency said.
"The U.S. Coast Guard stands ready to respond to Australia's request," Vice Adm. Paul F. Zukunft, the Coast Guard's Pacific area commander, said. "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.
"We are pleased to learn the passengers of the Akademik Shokalskiy have been transported safely off the vessel. 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 Polar Star had left its home port of Seattle early last month. One of its primary missions is to cut a channel in McMurdo Sound to resupply and refuel the U.S. antarctic program's McMurdo Station on Ross Island.