WELLINGTON, New Zealand -- Former American astronaut Buzz Aldrin, one of the first men to walk on the moon, has been evacuated by plane from the South Pole for medical reasons, officials said Thursday. He landed safely in New Zealand and is receiving treatment there.

Aldrin, 86, was seen smiling in his hospital bed in a photo posted on his Twitter account Thursday afternoon, along with a message that said he was “recovering well.”

Official statement about Buzz and his evacuation from the South Pole. He's recovering well in NZ. Full statement https://t.co/OacRI4577Z pic.twitter.com/QdrEaHuQHq — Buzz Aldrin (@TheRealBuzz) December 1, 2016

Aldrin “currently has fluid in his lungs but is responding well to antibiotics and being kept in overnight for observation,” said a statement posted on his website. “His condition is stable and his manager, who is currently with him, described him being in good spirits.”

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Aldrin had been visiting the South Pole as part of a private tourist group when his health deteriorated, the International Association of Antarctica Tour Operators said on its website.

It said he was taken as a precaution on the first available flight to McMurdo Station, a U.S. research center on the Antarctic coast. It described his condition as stable and said that his family had been informed of the situation.

The National Science Foundation, which manages the U.S. Antarctic program, described Aldrin as “ailing” and said he was flown on a ski-equipped LC-130 cargo plane to McMurdo. From there, he was flown to Christchurch, New Zealand, where he was transferred to a local medical facility for treatment, the foundation said.

Aldrin became the second man to walk on the moon in 1969 as part of the U.S. Apollo 11 mission.

In the years since, he has remained a vocal advocate of space exploration, even testifying before Congress last year in support of manned missions to Mars and the development of a human colony on the Red Planet.

Earlier this year, Aldrin wrapped up a non-stop 10-week book tour in the U.S. and the U.K. for a book of reflections entitled, “No Dream Is Too High: Life Lessons From a Man Who Walked on the Moon.”

He told “CBS This Morning” in July that while he’s proud of his role in space history, he doesn’t dwell in the past.

“The book is back then, but my life is right now. And right now, it’s about the future,” Aldrin said.