(CNN) -- Efforts to rescue a research crew aboard a ship stuck in ice off Antarctica stalled Thursday after sea ice conditions made a key element of the rescue plan risky, Australian maritime officials said.
The rescue plan called for a helicopter to ferry the passengers from the MV Akademik Shokalskiy to a Chinese vessel, where they would then board a barge to take them to an Australian icebreaker, the Australian Maritime Safety Authority (AMSA) said in a written statement.
But the shifting ice conditions prevented the barge from being able to reach the Chinese vessel, the statement said.
"Alternative measures to complete the rescue operation are now being investigated by AMSA and the ships involved," the statement said.
The news is the latest chapter in a saga that began Christmas Eve after the Russian-flagged MV Akademik Shokalskiy got stuck in 10 feet of ice.
Even if the rescue begins Friday, it will still be weeks before the research team will make it to Hobart, Australia, John Young of the Australian Maritime Safety Authority said.
"Mid-January is our best guess," Young told reporters on a conference call.
The rescue plan called for the helicopter, which can transport 12 people each trip, to ferry the ship's 52 passengers -- who include the research team and journalists -- to the Chinese icebreaker called the Snow Dragon, or Xue Long, the maritime agency said. The 22 Russian crew members of the Akademik Shokalskiy will stay aboard, it said.
The passengers are then to be transported by barge from the Chinese ship to the Australian icebreaker Aurora Australis.
That's because the Chinese helicopter can't land on the Australian icebreaker because of load restrictions, and ice conditions make it unsafe to land it next to the ship, AMSA said.
"The preferred option is to wait for conditions that will allow the rescue to be completed in a single operation to reduce unnecessary risk," the maritime agency said.
The master of the Akademik Shokalskiy has decided to keep the crew members on board until the pack ice eventually breaks up and allows the ship to move again, Young said. The vessel has enough supplies to keep the crew going for "a very long time," he said.
The planned helicopter rescue follows a failed attempt by the Chinese icebreaker, which made it six nautical miles from the trapped vessel before being stopped by the ice.
That was followed by an effort by the Australian icebreaker, which was forced Monday to suspend efforts to reach the expedition because of bad weather. The Aurora Australis got within 10 nautical miles of the ship before it turned back.
Over the weekend, an effort by the French icebreaker Astrolabe was called off by the maritime agency.
In preparation for the helicopter rescue, members of the research team as well as the crew of the Akademik Shokalskiy marked a makeshift helipad on the ice where the helicopter can land.
Video clips posted online by the research team showed people, with arms locked, walking to tamp down the snow.
"As we understand, the helipad was suitable yesterday and will be suitable today," AMSA's Richard Wallace said.
Once the passengers are safely aboard the Aurora Australis, the ship will complete a resupply mission to Casey Station, an Australian base in Antarctica, before making its way to Hobart, the maritime agency said.
The exploits of the research crew have gone viral, thanks in large part to Twitter and YouTube posts by those aboard the stranded vessel.
Chris Turney, an Australian professor of climate change at the University of New South Wales, has tweeted photos of the stranded ship, the crew and penguins, who he said -- according to one post on Twitter -- "to check out what's going on."
"The group on this ship is incredibly collegiate," said Alok Jha, a science correspondent for The Guardian newspaper, told CNN's Anderson Cooper 360. "There are a lot of skills and things people are sharing with each other."
Turney has said there are regular briefings on the status of rescue attempts, and in the meantime, people are doing what they can to keep busy. That includes yoga and Spanish classes, Jha and Turney said.
The group even managed to ring in 2014 with good cheer.
"We're the A, A, E who have traveled far, having fun doing science in Antarctica!" a dozen or so of them sang in a video posted on YouTube. "Lots of snow and lots of ice, lots of penguins, which are very, very nice!
"Really good food and company, but a bloody great shame we are still stuck here! Ice cold, cha cha cha! Ice cold, cha cha cha!"
CNN's Radina Gigova and Jethro Mullen contributed to this report.