The search is focusing on the Liberty Ridge area, on the northwest shoulder of the mountain, where the group was last heard from on Wednesday at 6 p.m. when they called in via a satellite phone and reported they were at the 12,800-foot level.
The climbers began their ascent on Monday and were due out on Friday but they never showed up, said Mount Rainier National Park spokeswoman Patricia Wold. They were scheduled to reach the summit of Mount Rainier on Thursday, with a day to climb down.
The group is made up of four clients led by two skilled climbing guides from Alpine Ascents International, which reported the party missing at 4:30 p.m. on Friday.
A small weather front that brought snow flurries and hail to the mountain moved in on Wednesday, Park Ranger Fawn Bauer said. The weather has been clear since then.
Alpine Ascents' director of programs, Gordon Janow, said he wasn't ready to release information about the climbers. "Let's hope they're found and that it goes well," he said.
Details - such as ages, gender or hometowns - for the climbers were not immediately available, Bauer said.
The U.S. National Park Service has a group of three climbing rangers heading to the area. Two climbing rangers on board a contract helicopter are conducting an air search and a U.S. Army Reserve 214th Air Division Chinook helicopter out of Joint Base Lewis McChord is also providing air support.
The command post for the search is set up at Longmire.
Some 10,000 people attempt to climb 14,410-foot Mount Rainier each year, with about half making it to the summit. The Liberty Ridge area is considered one of the more technical and advanced routes on the mountain.