Nepal commemorated the anniversary of the first ascent of Mount Everest on Wednesday amid a climbing season marred by the highest death toll in four years and a debate on whether the government should limit permits to prevent dangerous overcrowding on the world's highest peak.

Government officials said at an event in Kathmandu celebrating the successful climb of Edmund Hillary and Tenzing Norgay in 1953 that there were no plans to cap permits. Nepal, one of the world's poorest countries, takes in $300 million each year from climbing.

A record number of 381 permits were issued this year. Eleven people have died on Everest, including nine in Nepal, likely due to altitude sickness, which is caused by low amounts of oxygen at high elevation and can lead to headaches, vomiting, shortness of breath and mental confusion.

Because of the altitude, climbers have just hours to reach the top before they are at risk of a pulmonary edema, when the lungs fill with liquid causing respiratory failure. Mountaineers described traffic jams caused by exhausted rookies in the "death zone," the final phase of the ascent from Camp Four at 8,000 metres (26,240 feet) to the 8,850-meter (29,035-foot) peak.

The nine deaths this year on Nepal's side of the mountain included Don Cash, a sales executive from Utah, and Christopher Kulish, an attorney from Colorado, who both died on their way down from the summit.

Kulish, 62, had just reached the top with a small group, according to his brother, Mark Kulish. That earned him a place in the "Seven Summit Club" of mountaineers who have reached the highest peaks on every continent, his brother said.

Cash, 55, who also joined the Seven Summit Club with his climb, collapsed at the top and was given CPR and massages by his two Sherpa guides. He got up only to fall again in the same way at Hillary Step, the first cliff face down from the summit.

Two other climbers - from Ireland and Austria - died on the northern side of the mountain in Chinese territory, according to media reports.

On Wednesday, Nepalese government minister Gokul Prasad Baskota said the congestion on Everest wasn't due to the mismanagement of climbing permits but rather the inadequate training of some climbers.

Renowned mountaineer Um Hong-gil of South Korea, who was honoured by the Nepal government at the event commemorating the 66th Everest anniversary, said the number of climbers should be scaled back and only those with proper training and experience should be allowed.

"There should definitely be less permits issued and more experienced climbers on Everest," Um said.

He said the endeavour -- once only possible for well-heeled elite mountaineers -- has changed greatly since he first climbed Everest in 1988, in part because of advanced weather forecasting technology that more accurately predicts clear conditions, leading to pileups at the peak.

"Many people are now taking climbing Everest very lightly and as entertainment only, which they think they can do without much training," Um said.

The Nepal Mountaineering Association, an umbrella body of expedition operators, said it would push the government to require climbers to adequately prepare for what Um described as an extremely taxing physical and mental task.

"The government needs to come up with strict policies to control the inexperienced climbers from attempting to scale Everest," said the association's president, Santa Bir Lama.

Lama also faulted private trekking companies that are more focused on expanding their client base than safety.

He also said that government permits, which are often issued to climbers just days before their expeditions, should be issued months in advance to give climbers time to fully prepare.

A climber from Kashmir who returned to Kathmandu after a failed attempt on Everest agreed that there should be a standard that climbers must meet.

"People just throw the cash and get a permit to climb Everest because there are no criteria," said Rizza Alee. "Lots of people I saw were inexperienced."

Expedition operators said they do vet climbers' experience and ability before signing up them up and that even seasoned mountaineers sometimes lose their lives on Everest.

"In the mountains it is always unpredictable," said Mingma Sherpa of Seven Summits Treks, one of the biggest expedition companies in Nepal.

Sherpa said the government cannot limit the number of permits because of the lasting draw of the world's highest peak.

"People from all over the world would want to come visit Everest and that cannot be stopped," he said.