Six climbers on Mount Rainier likely fell more than 1,000 metres to their deaths in what would be among the worst alpine accidents ever on the iconic Washington mountain in the U.S.

A helicopter crew on Saturday spotted camping and climbing gear in the avalanche-prone area. It is believed the group fell 1,005 metres from their last known whereabouts of 3,900 metres on Liberty Ridge, Mount Rainier National Park spokeswoman Patricia Wold said in a statement.

"There's not a viable chance of survival," park Ranger Fawn Bauer told The Associated Press.

Search suspended

Air and ground searches were suspended late Saturday afternoon. The danger of falling rock and ice in the area where searchers picked up pings from the climbers' emergency beacons prevents a ground recovery effort.

"It would expose our rangers to pretty extreme conditions," Bauer said. "And, in all honesty, we may never be able to get on the ground there." 

Missing Rainier Climbers

'The mountain is so inaccessible and can be inhospitable. We can't always retrieve everybody who is lost there, unfortunately,' said Patti Wold, a spokeswoman with Mount Rainier National Park. (Lui Kit Wong/Associated Press)

Aircraft will survey the area periodically in the coming weeks and months, Wold said, but the possibility of recovering the six is uncertain.

The missing group includes four clients of Seattle-based Alpine Ascents International and two guides. They were due to return from the mountain on Friday. When they did not return, the climbing company notified park officials, Bauer said.

Officials have yet to finish family notifications, so the names of the climbers are unlikely to be released until Sunday.

"The climbing community is a small one and a close one and a loss of this magnitude touches many," Superintendent Randy King said in the statement.

The loss of life would be among the deadliest climbing accidents ever on the peak in the Cascade mountain range. In 1981, 11 people were killed during a guided climb when they were struck by a massive ice fall on the Ingraham Glacier. On Oregon's Mount Hood seven students from a college preparatory school in Portland and two adults died after they dug a snow cave during a sudden storm in 1986.

Glacier-laden peak

Mount Rainier, southeast of Seattle, stands at 14,410 feet and attracts thousands of climbers trying to reach its summit every year. It is popular with climbers of all abilities, from novices who take guided climbs to experienced alpinists who use the glacier-laden peak to train for attempted ascents on taller mountains in the Himalayas and other mountain ranges. Before this most recent accident the park service says 89 people have died trying to climb Mount Rainier since 1897.

Mount Rainier Fall

An active volcano, Mount Rainier rises 4,392 metres above sea level and, along with Mount Baker, dominates the Seattle skyline. (Ted S. Warren/Associated Press)

The search for the missing climbers focused on the northwest shoulder of the mountain at the Liberty Ridge area, near where they were last heard from, Bauer said. Saturday's search included a team of three climbing rangers on the ground and flyovers with a Hughes helicopter. An Army Chinook helicopter then joined the search from Joint Base Lewis-McChord. 

The group was scheduled to reach the summit of Mount Rainier on Thursday, with a day to climb down.

Snow flurries and hail hit the mountain Wednesday, Bauer said, but the weather has been clear since then.

Bauer said ground crews on Saturday checked "every possible area" where someone could have sought refuge in the storm.

Alpine Ascents' director of programs, Gordon Janow, said he wasn't ready to release information about the climbers.

In a statement from the park, the guides were described as skilled. In a blog post on the Alpine Ascents website Thursday, the post said the team had turned around near 4,000 metres during their attempt to reach the summit because of weather conditions.

Wold said the Liberty Ridge route the group were attempting is one of the more technical and advanced on Mount Rainier.