MELBOURNE, Australia — An Australian air crew flew an American from an Antarctic base to a New Zealand hospital in a rare midwinter rescue.

The Airbus A319 Long Range aircraft, with the call sign Snowbird 1, flew from the Australian city of Hobart to the U.S. McMurdo Station in Antarctica on July 31 in response to an “urgent request for assistance,” the jet’s Melbourne-based owner Skytraders said in a statement Thursday.

The jet landed after a five hour and 30 minute flight at the Phoenix Airfield near McMurdo in darkness and with temperatures as low as minus 43 C (minus 45.4 F), the statement said.

The American was flown on the same day to a hospital in Christchurch, New Zealand, as weather conditions at the Antarctic air strip worsened, said Skytraders, which is contracted by the Australian Antarctic Division.

The U.S. National Science Foundation told the Australian Broadcasting Corp. that the patient was admitted to the Christchurch Hospital in a “serious condition.”

The AAD said in a statement Friday the patient continued to receive medical treatment in Christchurch.

“This was a complex operation carried out in the depths of the Antarctic winter, and it highlights both the capability of our people and the strong partnerships that underpin Antarctic programs around the world,” the head of AAD, Emma Campbell, said.

New Zealand’s Health Ministry on Friday would not comment on the American’s condition or say whether the American remained in hospital.

The mission’s copilot, Louise Robertson, said conditions were close to the limit of the aircraft’s capabilities.

“We had some what’s called nautical twilight, which is a very minimal amount of light that is pretty much pitch blackness and also the extreme cold temperatures. We are right on the verge of the limitation of the aircraft,” Robertson told ABC.

“It was very close to being too cold,” she said. ”It got down to minus 43 (Celsius), which is the coldest I’ve ever felt. It was about 8 knots of wind, so quite a bit of wind-chill as well.”

Robertson said plans to fly to the base on the Ross Ice Shelf a day earlier were aborted due to a snow storm.

“There … was really just such a narrow window of opportunity,” Robertson said.

“To get there in complete darkness in these extreme cold temperatures is very, very rare. I believe it hasn’t been done before,” she added.

The sun last set at the geographic South Pole on March 23 and will not rise until Sept. 21.

The New Zealand Air Force evacuated a New Zealand citizen working on the U.S. Antarctic Program from the Phoenix Airfield in a C-130 Hercules in a medical emergency in April, which is the Southern Hemisphere autumn.

In August last year, the final month of the Southern Hemisphere winter, New Zealand used the same type of four-engine turboprop transport aircraft to evacuate three people on a flight from McMurdo for medical treatment.

McMurdo shares its airstrip with New Zealand’s nearby Scott Base.