Two prominent American climbers exploring a region of unclimbed 20,000-foot peaks in southwest China were last heard from in November and are presumed missing.

Fellow climbers in the United States say they and American and Chinese officials in China's Sichuan province have organized searches for the two: Christine Boskoff, one of the world's top female high-altitude climbers, and Charlie Fowler, a well-known climber, mountain guide and photographer.

Boskoff has ascended six of the world's 26,000-foot peaks, including Mount Everest. She owns Mountain Madness, a Seattle adventure travel company formerly owned by Scott Fischer, one of the guides who died on Mount Everest in the 1996 season portrayed in Jon Krakauer's best-selling book, "Into Thin Air."

Fowler, who is from Colorado, is an expert on climbing in southwestern China. He has guided climbers up Everest and has conquered several other of the world's tallest and most difficult peaks.

Click here to go to FOXNews.com's Asia Center.

Boskoff and Fowler left for China in the early fall. Boskoff guided three clients to the summit of China's 26,906-feet Cho Oyu in early October.

Boskoff and Fowler were last heard from in early November, after a first ascent up the North Face of the previously unclimbed 19,094-foot Yala Peak, known to locals as Haizishan. They were due back in Denver on Dec. 4.

"I'm having a great time and love the country, mountains and people here," Boskoff said in an e-mail on Nov. 7 to the Mountain Madness office.

A day later in the last e-mail the office received from her, Boskoff wrote: "We'll be leaving tomorrow and we'll be back in Internet contact in two weeks."

Authorities have found no evidence the pair ever made it to peaks in another part of China that they talked about exploring in their last e-mails.

Mark Gunlogson, president of Mountain Madness, said Thursday that ground searches were being launched in other regions.

"We're mobilizing a search and rescue crew on the ground, along with assistance from the U.S. consulate and Chinese authorities," he said. "The hope is that they're sitting in some village drinking yak butter tea, waiting for the weather to clear."