Story highlights The U.S. ship should take a week to reach Commonwealth Bay, Australia says

U.S. Coast Guard Cutter Polar Star is heading toward Antarctica

Its aim is to help free Russian and Chinese ships stuck in ice there

Governments of Australia, China and Russia asked for the help

At the request of the Australian, Russian and Chinese governments, the U.S. Coast Guard is stepping up to help break up ice off Antarctica that has ensnared a pair of ships.

The Coast Guard Cutter Polar Star had been heading to that area anyway, having left its home port of Seattle early last month to eventually break through sea ice and refuel the U.S. Antarctic Program's McMurdo Station on Ross Island.

Now the icebreaker is retooling to help the Russian ship Akademik Shokalskiy and China's Xue Long due to "sufficient concern that the vessels may not be able to free themselves from the ice," the Coast Guard said Saturday in a statement.

The Polar Star, currently in Sydney, will take on supplies and head out Sunday on what should be a seven-day voyage to the ships in Commonwealth Bay, according to the Australian Maritime Safety Authority.

"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," said Vice Adm. Paul F. Zukunft, the U.S. Coast Guard's Pacific commander.

The Australian agency formally requested the Americans help on Friday. The Coast Guard noted that the governments of Russia and China also asked for U.S. assistance.

The Akademik Shokalskiy has been stranded since December 24, 2013.

Earlier this week, a helicopter ferried 52 passengers from the MV Akadmik Shokalskiy to the Australian icebreaker Aurora Australis.

The Akadmik Shokalskiy had been trapped in unusually deep ice since Christmas Eve with scientists, journalists, tourists and crew members on board.

Twenty-two Russian crew members are still on the Akademik Shokalskiy, waiting for either the ice to shift or for outside help.

Xue Long is a Chinese icebreaker that sent out the helicopter Thursday that airlifted several dozen passengers from the Akademik Shokalskiy to safety.

But after that happened, the Chinese vessel itself got stuck in the ice, according to the Australian Maritime Safety Authority.

The Xue Long's captain told AMSA that his ship is safe, has plenty of food and supplies and did not need immediate assistance.

The U.S. Coast Guard's "only active heavy polar icebreaker," the 399-foot long Polar Star recently completed a three-year, $90 million overhaul.

Capable of traveling at speeds of 18 knots (21 mph), the ship can continuously break through 6 feet of ice while traveling 3 knots. With its reinforced hull and special bow, the Polar Star can bust through as much as 21 feet of ice at a time.

After its new mission, the U.S. Coast Guard vessel is set to continue to its original mission in McMurdo Sound.