Passengers aboard the Akademik Shokalskiy, the ship stuck in ice off the coast of Antarctica since Christmas Day, were told on Sunday morning they would have to be evacuated by air if icebreaker ships could not get to them within 48 hours.

The Russian-operated ship has about 50 passengers – including scientists and paying members of the public – and 20 crew on board. It became stuck in the ice near Cape de la Motte in east Antarctica, abouit 1,500 nautical miles from Hobart in Tasmania, after strong blizzards hit the vessel on Christmas Eve. Surrounding pack ice was pushed by strong winds against the Antarctic landmass, pinning the Shokalskiy in place.

On Friday, the Chinese icebreaker Xue Long tried to battle through the thick ice towards the Shokalskiy but had to turn back after 12 hours and within 8.5 nautical miles of the Russian vessel, because the going was too difficult. The Aurora Australis will arrive at the edge of the sea ice, which is about 20 nautical miles from the Russian ship, in the early hours of Monday local time (about 1pm Sunday GMT).

“What we're depending on is the extra grunt of the Aurora Australis,” said Greg Mortimer, co-leader of the Australasian Antarctic Expedition (AAE), which has chartered the ship. “It's a more traditional icebreaker hull, which is like a bathtub with a big engine inside it – it can push over the ice and lay down on top and work its way like that.”

Until the ship gets into position, it is unknown whether it will be strong enough to crack through the ice – which is four to five metres thick in places after storms in the area last week – and make it to the Shokalskiy.

If that proves impossible, the only option would be air evacuation.

“We're always making contingency plans,” Mortimer said. “That would happen by the Chinese vessel sending their helicopter to us, us preparing a helipad on the ice next to the ship and flying passengers from that ice onto the other vessels. Then taking them home via the Ross Sea or [Australian Antarctic base] Casey base by ship.”

Those on board the Shokalskiy will know within 12 hours of the arrival of the Aurora Australis whether the icebreaking mission is likely to be successful. Mortimer said the decision to evacuate would be in the hands of the captains of the icebreakers.

On Sunday afternoon, the Xue Long sent a helicopter to the Shokalskiy to survey the sea ice around the ship and look for any open water in the area.

Mortimer said the ship was safe and there was no threat to life or limb.

“The pressure at this point in time is one of time – that artificial contrivance of, well, we must get out of this situation as quickly as we can. But we don't have to, we're OK.”

A helicopter from the Chinese icebreaker Xue Long runs reconnaissance over the Akademik Shokalskiy. Photograph: Laurence Topham Photograph: Laurence Topham/Guardian

That would change, he said, if an iceberg began moving towards the ship. The closest icebergs are several nautical miles away at present. If one came close, the Shokalskiy would have a day or two's notice to carry out any necessary evacuation.

When it got stuck the Shokalskiy was just over two weeks into its month-long expedition, from Bluff in New Zealand to Commonwealth Bay in east Antarctica. The passengers on board are following in the footsteps of the great Antarctic explorer and scientist Douglas Mawson, leader of the original AAE of 1911, repeating his wildlife, ocean and weather observations to build a picture of changes over the past 100 years.

Over the weekend, members of the AAE were allowed off the vessel to take scientific samples of the ice, build igloos in the fresh snow or just stretch their legs and take pictures in the sunshine. The mood on board has remained calm, with expedition leaders regularly briefing the rest of the passengers about the various options to get them out of the ice.

Mortimer, a veteran of Antarctica with more than 100 visits to the continent under his belt, said he was not surprised by the difficulty the Shokalskiy has faced this week.

“The combination of elements is really unfortunate – a couple of blizzards and many, many days blowing in the wrong direction has piled heaps of trouble on our shoulders,” he said. “The power of the forces at work, that's the constant reminder – how overwhelmingly powerful the natural forces are here. That's the fearsome, gnarly-teeth side of Antarctica and its great beauty as well, its allure.”