DENVER Efforts to evacuate a sick American physician from Antarctica have been delayed for another 24 hours because of snow that made landing an aircraft at the South Pole impossible, his employer Raytheon Polar Services of Colorado said on Monday.

According to Reuters, Ronald Shemenski, 59, the only physician at the Amundsen-Scott South Pole Station, had a gall bladder attack and has been diagnosed with pancreatitis which could become life threatening.

Eighteen months ago another American physician Dr. Jerri Nielsen was evacuated after she discovered a tumor that was diagnosed as breast cancer.

Two twin Otter planes left Punta Arenas, at the southern tip of Chile on Saturday and landed safely at Rothera, a British military base on Adelaide island.

One of the planes was supposed to make the arduous 10-hour flight to the station to pick Shemenski up, but plans to leave on Sunday were scuttled because of bad weather, Elaine Hood, spokeswoman for the Colorado company said.

"Hopefully, they'll fly tomorrow at 10 a.m. MDT (noon EDT/1600 GMT)," Hood said.

Physicians decided the best course of action was to evacuate Shemenski after his medical problems arose, but that is a tricky proposition this time of year with low temperatures and near total darkness at the bottom of the world.

"Ron is not gravely ill now," his brother Dr. Robert Shemenski said in a statement posted on Raytheon's Website.

Raytheon Polar Services, of Englewood, Colo. operates the United States Antarctic program under contract with the National Science Foundation.

Bad weather has delayed another evacuation effort of four ailing Americans from another site in Antarctica, McMurdo base.

A New Zealand Air Force plane departed on Tuesday morning to carry out the evacuation. They are suffering from unspecified complaints.

"The plane left on time, the weather report is good and at this stage we expect a smooth operation," New Zealand Antarctic Institute spokeswoman Vivienne Allan told Reuters.

The Hercules aircraft, which flew out from the south island city of Christchurch, had been expected to undertake the evacuation on Monday but was delayed by high winds and the potential for snow flurries, she said.