Eight mountain climbers from the same expedition group, including two Americans, have gone missing in the Indian Himalayan Mountains, triggering a desperate search-and-rescue effort.

The group, led by notable British climber Martin Moran, left Munsiyari, India, on May 13 to set out for the Nanda Devi base camp, according to Govind Prasad, from the Pithoragarh, India, Disaster Management Office.

The group was reported missing on May 31, according to Prasad.

At 25,643 feet, Nanda Devi is the 23rd-highest mountain in the world and the second-highest in India.

The eight climbers who are missing are: Moran, John McLaren, Rupert Whewell and Richard Payne, all from the United Kingdom; Ruth McCance, from Australia; Chetan Pandey, an Indian from the Indian Mountaineering Foundation; and Anthony Sudekum and Ronald Beimel, both from the U.S.

"The ‘British Association of Mountain Guides’ (BMG) have been made aware of an incident on or near Nanda Devi East where BMG member, IFMGA Mountain Guide, Martin Moran was leading six clients and an Indian National," British Mountain Guides, a group that trains and assesses guides, said in a statement. "The BMG is assisting where possible and is in contact with the Indian authorities."

Fellow British climber Nigel Vardy, who was once stranded on Mount McKinley, the U.S.'s highest peak, and had his toes, fingers and nose amputated due to frostbite, is a friend of Moran. He called him "one of the best guides in the U.K." and "incredibly skilled" in an interview Sunday with ABC News.

"I believe this is the third time Martin’s led an expedition to Nanda Devi and I believe this was an unclimbed peak on the mountain," Vardy said. "Nobody has actually ever set foot on the summit of that peak."

Moran founded the climbing group, Moran Mountain, which said in a statement on Facebook, "We are working with the authorities and the British Association of Mountain Guides to gather information regarding the Nanda Devi East expedition team. Out of respect for those involved and their families, we will be making no further comments at this time. The BMG will release a further statement as and when more information is available."

The U.S. Department of State could not confirm the men were missing, but said it was aware of the reports.

"We are aware of reports of two U.S. citizens missing in India," a State Department official told ABC News. "The U.S. Department of State and our embassies and consulates abroad have no greater responsibility than the protection of U.S. citizens overseas. We stand ready to provide appropriate assistance to U.S. citizens in need, and to their families. We are monitoring the situation but have no further comment at this time."

A rescue team was sent to the Nanda Devi base camp, including personnel from the State Disaster Relief Fund, Indo Tibetan Border police force and a team of doctors, according to Prasad. A helicopter was sent as well, but has been unable to land so far because of adverse weather conditions.

"Martin’s a great planner so I know he’s been planning this expedition for a long time," Vardy said. "Weather conditions change and often very quickly and Martin would have known that."

The dangers of climbing have received greater scrutiny in recent weeks due to the deaths of almost a dozen people climbing Mount Everest, which is also located in the Himalayas.

"Having been reported missing in the mountains myself before, and I was fortunate to come out in one piece, I just pray that Martin and the team are in a similar position,” Vardy said.

ABC News' Sreya Banerjee, Megan Barkett, Conor Finnegan, Darren Reynolds and Matt Foster contributed to this report.