Mr Apa Sherpa, 49, who lives in the United States, reached the 8,850-metre (29,035-foot) peak along the Southeast Ridge route, pioneered by New Zealand's Sir Edmund Hillary and Sherpa Tenzing Norgay in 1953.

'Climbing Everest is a very difficult thing,' said Mr Ang Tshering Sherpa, chief of the Asian Trekking Agency that sponsored the Eco Everest Expedition with which Apa climbed.

'It is becoming more and more challenging because of climate change that has melted ice, exposed steep rocks and widened crevasses.'

Mr Apa, who first reached the summit of Everest in 1990, was born in Solukhumbhu district, home to Mount Everest, but now lives in the Salt Lake City, Utah.

He carried a special metal vase containing auspicious Buddhist offerings to the world's highest point, hoping to draw international attention to the effects of climate change on the Himalayas.

Environmental activists say the Himalayan glaciers are rapidly shrinking due to climate change, threatening the lives of millions of people who depend on them for water.

More than 3,000 people have climbed Everest from the Nepali and Tibetan sides since 1953. -- REUTERS