Story highlights Chinese ship can't break the ice, but remains nearby to aid rescue

A French icebreaker ship that was en route had its mission suspended

The trapped research vessel is carrying 74 tourists and scientists studying climate change

An Australian icebreaker also is en route

A Chinese ship trying to reach a trapped expedition vessel in Antarctica has turned back.

The icebreaker Xue Long, or Snow Dragon, was just six nautical miles away from the Russian-flagged vessel when the captain decided the ship could not get any closer, the Australian Maritime Safety Authority said Saturday.

The Snow Dragon went back to open water and remains in the vicinity of the stuck ship, the Akademik Shokalskiy, to provide support, said Andrea Hayward-Maher, spokeswoman for the AMSA. The Chinese vessel has a helicopter on board that could assist in evacuation.

A French icebreaker was en route to assist, but AMSA called off that vessel's mission at midday Saturday.

The rescue icebreakers were battling the planet's coldest environment in trying to reach the stranded Russian-flagged ship, whose 74 researchers, crew and tourists remained in good condition despite being at a frozen standstill since Monday.

AMSA said another icebreaker, the Aurora Australis, was en route and was expected to arrive late Sunday.

"Really, it's just a matter of the Aurora Australis getting down there and assessing the situation to see if it has any capability of breaking through the ice further than the Chinese vessel could and, if not, the aerial transfer of passengers on board may be a possibility," Hayward-Maher said.

Hayward-Maher said the Australian ship has icebreaking equipment the Chinese and French vessels don't have.

"The Chinese vessel and the French vessel are rated to a depth of one meter, which means they are capable of breaking through ice somewhere in the vicinity of a meter," she said. "The Aurora Australis has an ice rating of 1.35 meters.

"Some reports say that the ice is at least 2 meters deep. It's a possibility that the Aurora Australis might not be able to break through that type of ice, anyways."

The expedition ship is carrying scientists and passengers led by an Australian climate change professor.

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Spirits were high Saturday aboard the Akademik Shokalskiy.

"The vessel is fine, it's safe and everyone on board is very well," expedition leader Chris Turney, a professor of climate change at University of New South Wales in Australia told CNN. "Morale is really high."

The ship got stuck in the ice on Monday night -- 15 days after setting out on the second leg of its research trip.

According to Turney, the ship was surrounded by ice up to nearly 10 feet (3 meters) thick. It was about 100 nautical miles east of the French base Dumont D'Urville, about 1,500 nautical miles south of Hobart, Tasmania.

On Christmas morning, the ship sent a satellite distress signal after conditions failed to clear.

The crew had a "great Christmas" despite their situation, Turney told CNN. He said crew members have used the delay to get more work done.

"We've just kept the team busy," he said.

The expedition is trying to update scientific measurements taken by an Australian expedition led by Douglas Mawson that set out in 1911.

The expedition to gauge the effects of climate change on the region began November 27. The second, and current leg of the trip, started December 8 and was scheduled to conclude with a return to New Zealand on January 4.

Turney said the ship should still be back in New Zealand on time.