Three climbers from Brazil, Russia and France died while descending Mount Everest on separate expeditions in the past week, a Chinese official said Tuesday.

The climbers, whose names weren't released, reached the summit of Everest and died of exhaustion on the way down, said Zhang Mingxing, secretary-general of Tibet Mountaineering Association.

"It is easy for climbers to feel exhausted after they have spent too much energy to reach the peak. They have to face the severest test from nature and their own physical strength," he said by phone from Lhasa, the Tibetan capital.

Last week, officials said 42 climbers took advantage of improved weather to reach the summit from its Nepalese side.

American, Australian, Austrian, British, Canadian, German, Korean, Philippine, Polish, Spanish and Swiss climbers, along with their Sherpa guides, reached the 29,035-foot summit, said Rajendra Pandey at Nepal's Ministry of Tourism in Katmandu.

May is considered the best month to climb Everest. Climbers in Nepal have to complete their mission by May 31 before the weather deteriorates during monsoon season.

Since Everest was first conquered by New Zealander Edmund Hillary and Sherpa Tenzing Norgay on May 29, 1953, more than 1,400 climbers have scaled the peak, and some 180 people have died trying.