A Sherpa guide completed 21 hours at the summit of Mount Everest today, setting what is likely a record for the longest stay atop the world's tallest mountain.

Moreover, Babu Chhiri Sherpa, 33, did not use bottled oxygen during his overnight stay, said Shailendra Sharma, chief of the mountaineering department at Nepal's Tourism Ministry.

Chhiri reached the 29,028-foot summit at 10:30 a.m. Thursday (12:45 a.m. Wednesday EDT), his eighth successful ascent. He and two colleagues pitched a specially designed tent before the others left.

He hoisted a national flag and sang Nepal's anthem, "Praise the King and the Country."

"Chhiri said on the radio that he wants to present the flag and recording of the national anthem to King Birendra," said Ang Babu Sherpa of Nomad Expeditions, which provided the equipment for the venture.

Chhiri left the summit at 7:55 a.m. today (10:10 p.m. Thursday) for the South Col camp at 26,400 feet, where his friends were waiting.

No official records have been kept for the longest time spent at Everest's summit, but high winds, low air pressure and rapid changes in extreme weather conditions usually force climbers to retreat after a few minutes.

Chhiri's climb brought him closer to the record for the most successful ascents of Everest. Other Sherpas have climbed the mountain nine and 10 times.

Western climbers often rely on bottled oxygen to help them breathe on the mountain's upper reaches, though the canisters are heavy and cumbersome. Most Nepalese Sherpas go without, but few have dared spend so much time at the summit, where air pressure is low and breathing is difficult.

Sherpas, who live at the foot of the Himalayas, are known as "tigers of the snows." Renowned for their mountaineering skills, they were mostly yak herders and traders until Nepal opened its borders to tourism in 1950. Their stamina and knowledge of the mountains makes them expert guides and porters.

Eight Western climbers and 10 Sherpa guides took advantage of a break in the weather on Wednesday to become the first to reach the summit this year.

Arvin Timilsina, a 15-year-old Nepalese student trying to become the youngest person ever to scale Everest, abandoned his bid Wednesday because of pain in his eyes, the Tourism Ministry said.