More than 50 climbers reached the top of Mount Everest Friday at the start of a two-day window that has raised fears of perilous overcrowding on the world's highest peak after four deaths last week.
The 48-hour stretch of forecast good weather was expected to see more than 200 climbers try a final push to the 8,848-metre (29,029-foot) summit, despite warnings of potentially deadly bottlenecks in the "death zone" above 8,000m.
"So far 52 people have summited and there were a total of 150 ready to climb at camp four," said tourism ministry official Tilak Pandey.
"Yesterday only half went up because they were fearing traffic jams and those remaining will start their ascent (Friday) evening and will be back by tomorrow."
Mountaineers are taking advantage of the spring climbing season, when jet streams that rage over Everest for most of the year abate for a few weeks.
Four climbers from Germany, South Korea, China and Canada died while descending from the crowded summit area last weekend, which saw 150 people reach the top of the world before a severe windstorm set in.
Experts say the sheer numbers of climbers exacerbates the already substantial dangers of tackling Everest, which has now claimed more than 220 lives -- half of those in the past 20 years.
"Two hundred people climbing the mountain is too many for one weekend. Twenty-five to thirty a day is okay but 200 is too many," said Pemba Dorje Sherpa, who holds the eight-year-old record for the fastest ascent of Everest.
"You have many people waiting and waiting. They spend too long waiting at the top and they get frostbite. Waiting around on Everest is dangerous. Running out of oxygen can be a big problem."
Blog posts and reports sent by satellite telephone from base camp spoke of queues at precarious ridges and jostling as people tried to pass each other.
"The problem is not in fact that too many people might be on the mountain but rather too many people attempt to reach the summit on the same day, leading to overcrowding in the highest parts," Dawa Steven Sherpa told AFP by email from the base camp.
Some have pointed a finger at the increasing number of commercial expeditions shepherding paying climbers up the mountain.
Clients fork out about $25,000 to expedition organisers plus between $10,000 and $25,000 for an Everest permit, and some have been accused of ignoring their guides when advised to turn back.
Traditionalists also worry about the growing tendency of expeditions to set records and achieve "firsts".
This year's crop of summiteers has included the oldest woman ever to achieve the feat, 73-year-old Japanese Tamae Watanabe, who beat her own record.
Everest is a lucrative revenue earner for the Nepalese government and officials in Kathmandu have played down concerns about the numbers of climbers.
"I don't think that the overcrowding has led to deaths. It depends on the weather and this season it has been bad," said tourism ministry spokesman Bal Krishna Ghimire.
Among those reaching the top on Friday was Briton Kenton Cool, who fulfilled an 88-year-old promise to carry an Olympic gold medal to the summit.
The medal was one of 21 awarded to members of a British Everest expedition at the 1924 Winter Olympics, in an era when mountaineering was included as an Olympic sport.
Their 1922 expedition had come within 500 metres of the summit, but failed in three attempts to reach the top.
Lt. Col Edward Strutt, a member of the team, had pledged that at the very next opportunity one of the gold medals would be taken to the top of the world -- a promise that, until now, had remained unfulfilled.
For Cool, 38, it was his 10th successful ascent of Everest, breaking his own British record.
Since the first ascent on May 29, 1953, by Sir Edmund Hillary and Tenzing Norgay, about 10,000 people have attempted to climb the ultimate peak, almost 4,000 successfully.