Two American mountain climbers and a Canadian climber are missing after failing to return from their attempted summit of New Zealand’s highest peak on Monday, officials said. 

Deteriorating weather conditions and treacherous terrain on Aoraki, also known as Mount Cook, have hindered the search for the two Americans – Kurt Blair, 56, from Colorado, and Carlos Romero, 50, of California – and the Canadian man whose identity is being withheld at his family’s request, New Zealand Police said Wednesday.

The climbers flew to a hut partway up the 12,218-foot alpine mountain on Saturday to begin their ascent via Zurbriggen Ridge, according to police Inspector Vicki Walker, Aoraki area commander. When the men failed to arrive for their flight out on Monday morning, they were reported overdue. 

In the hours after the climbers were reported missing, teams recovered several climbing-related items believed to belong to the three men, Walker said. But there was no sign of the climbers.

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Kurt Blair

Kurt Blair, 56, from Colorado, is one of three climbers missing on New Zealand's highest peak, Aoraki. (Instagram/ Kurt Blair)

While the climbers have yet to be confirmed dead, police said they have "grave concerns for the three men" as heavy rain and snowy conditions forced the search operation to pause since Monday night. Police said the search would resume once the weather clears, which was unlikely before Thursday.

Carlos Romero

Carlos Romero, 50, of California, is one of three climbers missing on New Zealand's highest peak, Aoraki. (Instagram/ SWS Mountain Guides)

The Silverton Avalanche School, where Blair worked, said authorities informed them that the three men appeared "to have taken a fatal fall from high upon the peak."

"He was the nicest guy you’d ever share a rope or trail or skin track with, and his humility, competence and polite nature made him a client and student favorite," the school said of Blair. "For those of us who have logged significant time in the backcountry with Kurt, the loss of such a wise and steady partner is devastating."

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SWS Mountain Guides, where Romero was employed, said he was "a beloved guide, educator and mentor" who was highly respected for his skills as a mountain guide.

Both Blair and Romero are certified alpine guides, according to the website of the American Mountain Guides Association.

Aoraki

Aoraki, also known as Mount Cook, pictured center, is New Zealand's highest peak. (AP Photo/Mark Baker, File)

Aoraki is a popular peak that is part of the Southern Alps that runs the length of New Zealand's South Island. It is known for both its scenic beauty and technically difficult terrain that boasts crevasses, avalanche risk, changeable weather and glacier movement.

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More than 240 deaths have been recorded on the mountain and in the surrounding national park since the start of the 20th century.

The Associated Press contributed to this report.