A Chinese icebreaker trying to reach a Russian ship trapped in Antarctica has been halted by thick ice within sight of the stricken vessel.
The Snow Dragon was one of three icebreakers sent to free the MV Akademik Shokalskiy, which became stranded south of Tasmania on Christmas Eve.
The vessel had become embedded in ice after a sudden change in the weather froze the sea around it.
"Since the thick ice exceeds the ship's ice breaking capabilities and an upcoming cyclone will exacerbate icy conditions, we have to temporarily stall the ship," Snow Dragon captain Wang Jianzhong said.
The trapped ship left New Zealand on on a privately funded expedition to commemorate the 100th anniversary of an Antarctic journey led by famed Australian explorer Douglas Mawson.
The ship's 74 passengers include scientists and tourists, many of them Australian, and 22 Russian crew members.
The Australian Maritime Safety Authority (AMSA), which is coordinating the rescue, said the Snow Dragon would remain on standby until an Australian icebreaker, the Aurora Australis reaches the MV Akademik Shokalskiy.
The Snow Dragon has a helicopter on board that can be used to rescue passengers if the Aurora Australis can not break through the ice, said an AMSA spokeswoman.
"The Aurora Australis is expected to arrive at the scene on Sunday evening. It's pretty slow going out there."
Chris Turney, an Australian professor who helped organise the voyage on the Russian ship, earlier posted a photograph apparently showing the Chinese vessel, a speck on the horizon beyond an expanse of ice.
"Sorry to report the Snow Dragon couldn't get through but standing by for other vessel to help," Professor Turney said via Twitter.
The Russian embassy in Australia has been in constant contact with the captain and said everyone on board was in good health and there was "no threat to their lives or safety".