A search was under way Friday for a 57-year-old climber missing on Mount Rainier, Mount Rainier National Park authorities said.

Park officials said Eric Lewis, of Duvall, Washington, was ascending the Gibraltar Ledges Route on Thursday in poor weather. His two climbing companions stopped to rest and when they pulled in the rope to regroup they discovered that Lewis had unclipped from the rope and was no longer with them, a release from the park said.

The two other climbers immediately established anchors in the snow and swept the length of the rope across the slope below them, but were unable to find their climbing partner. The two climbers returned to Camp Muir at 10,200 feet and climbing rangers initiated a search for the missing climber. Climbing rangers ascended to the summit late Thursday afternoon, but found no signs of Mr. Lewis, the park reported.

Search efforts expanded Friday, with park climbing rangers and commercial climbing guides from Rainier Mountaineering, Alpine Ascents, and International Mountain Guides joining the search. Two helicopters were also called in, a Chinook from Fort Lewis and a MD-530 with Northwest Helicopters in Olympia, the park reported. The weather was overcast, with a heavy cloud layer at 8000 feet.

Searchers did locate Mr. Lewis' backpack (with climbing harness and shovel) at 13,600 feet, and a snow cave at 13,800, the park reported.

"We have a dozen skilled climbers on the mountain and at least 20 others providing other types of support. We're doing everything we can to find him and get him down safely," said search Incident Commander Glenn Kessler.