A 51-year-old Nepalese climber scaled Mount Everest for the 21st time on Wednesday, extending his own record for the number of successful summits on the world's highest mountain, a spokesman said.

Apa Sherpa reached the peak at 9:15 am (0345 GMT) on Wednesday morning.

"He along with five other climbers had left camp four last night at 10 pm and all of them made it to the top," said Ang Tshering Sherpa, chairman of the expedition company Asian Trekking Private Limited.

The climber, dubbed the "Super Sherpa" for the apparent ease with which he climbs the mountain, dedicated his latest expedition to the impact of climate change on the Himalayas.

His success comes after tragedy earlier this week when 82-year-old former Nepalese foreign minister Shailendra Kumar Upadhyaya died in his attempt to become the oldest person to climb the mountain.

Upadhyaya died on Monday afternoon, hours after arriving at camp one in his bid to raise awareness about the capabilities of elderly people.

The oldest successful climber of Everest is Min Bahadur Sherchan, who scaled the mountain at the age of 76 three years ago.

Around 3,000 people have made it to the top of Everest since Edmund Hillary and Tenzing Norgay became the first to conquer the 8,848-metre (29,028-foot) peak in 1953.

Sherpa is leading the Eco Everest Expedition 2011, which aims to collect four tonnes of rubbish under a "Cash for Trash" programme funded by a private trekking company.

His first expedition to the top of the mountain was more than 20 years ago in 1990.

"If my ascent would promote the cause and help protect the mountain, I am always ready to climb," Sherpa told AFP before his flight to the Everest region.

The summit season on Everest begins in late April and May when a small window between spring and the summer monsoon offers the best conditions for making the ascent.