Ruapehu climber's leg amputated

Ash and a lahar are visible at the summit of Mt Ruapehu today. Photo / Alan Gibson

A climber who was "seconds from death" after being crushed in last night's Ruapehu eruption has had his right leg amputated below the knee but has had a "miracle" recovery.

Scores of people fled from the mountain last night after the eruption, which shook the volcano about 8.20pm and was witnessed by airline pilots.

The volcanic blast wiped out a monitoring hut near the crater lake, sending two muddy torrents down the skifields.

William Pike, a 22-year-old primary school teacher from Auckland, was in the Dome Vally Hut with three companions when a rock crashed through the roof and fell on him.

Mr Pike's friends were unable to move the rock and a Whakapapa Ski Field vehicle was called and freed him. The Taupo Lion Foundation rescue helicopter airlifted him to Taumarunui Hospital and then Waikato Hospital.

After four hours of surgery this afternoon, Mr Pike has regained consciousness. He is still suffering the affects of hypothermia and has damage to his left leg.

Dr John Bonning, the Waikato Hospital emergency department doctor who treated William at Taumarunui Hospital and then at Waikato said he was "amazed" at William's recovery.

"The fact that he's recovered is a miracle. He has recovered from the worst degree of metabolic derangement that I have ever seen. His body had pretty much shut down and he was so close to death ... literally seconds from death."

Dr Bonning said William's body temperature was 25 to 26 degrees Celsius and he was dangerously close to a cardiac arrest.

"For the majority of the night he was a hair breadth away from dying. It brought tears to my eyes to see him just now. He was so lucky it was just his legs.

"If there'd been any delays in any stage of the process, he would have been dead. Someone was with him every step of the way," said Dr Bonning.

"I congratulate everybody for what they did - to get him off the mountain, to Taumarunui, To Waikato. A young life with so much potential has not been wasted."

Mr Pike's parents Barry and Tracy said their son was a passionate climber.

"He lives to climb. He was in a place that he loved. He is a very conscientious climber and an incredibly active person," said Mrs Pike this morning.