(Adds official comment, accounts)
* Accident hits guides making path for climbers
* Search called off for the night
* About 100 climbers cut off above avalanche
By Gopal Sharma
KATHMANDU, April 18 (Reuters) - An avalanche sweeping down Mount Everest killed 12 Nepali guides on Friday at the start of the main climbing season, the tourism ministry said, in what may be the deadliest single incident on the world's highest peak.
The avalanche hit the most popular route to the summit. Three Nepali guides were injured, while four people are still missing and presumed buried under snow, the ministry said.
Friday's avalanche was the first major one on Mount Everest during this year's climbing season, when hundreds of foreign and Nepali climbers will flock to the mountain to attempt to reach its 8,850 meter (29,035 feet) peak.
The Himalayan Guides, a Nepali hiking group, said six of its sherpas had gone ahead of the climbers they were accompanying to fix ropes and crack snow and ice to carve out a trekking route when they were caught in the avalanche and died.
"They were very strong and skilled climbers. It is a natural disaster and no one could do anything about it," Ishwari Paudel, the owner of the group, said in Kathmandu. The other victims were working for other mountaineering groups.
More than 4,000 climbers have scaled Everest's summit since it was first climbed by Sir Edmund Hillary and Tenzing Norgay Sherpa in 1953. The route they took along the South Col was the one hit by the avalanche on Friday.
Nearly 250 people have died on Everest, which is on the border between Nepal and the Chinese region of Tibet and can be climbed from both sides. Nepal is home to eight of the world's 14 highest peaks.
The search for those still missing has been called off for the night and will resume on Saturday, Lakpa Sherpa of the Himalayan Rescue Association told Reuters from Base Camp.
OTHER CLIMBERS CUT OFF
The avalanche hit the sherpa guides between Base Camp and Camp 1 at around 6:30 a.m., eyewitnesses and officials said. It occurred in the upper reaches of the Khumbu Icefall, a dangerous section known for frequent avalanches, Sherpa told Reuters.
"An estimated 100 sherpas or Westerners were estimated to be above the impact area and are cut off from returning to Base Camp until a new route can be put in," mountaineer and blogger Alan Arnette wrote from the scene, adding this could take days.
The rising number of tourists attempting to climb Everest in recent years has raised concerns about both safety and environmental damage, although Nepal still plans next year to cut fees for those wishing to do the trek.
Nepal's Tourism Ministry has issued permits to 334 foreign climbers to scale Everest this season, up from 328 for the whole of last year. An equal number of guides also climb the mountain to help the foreign mountaineers.
A travel blog for 67-year-old Ed Marzec, a Californian attempting to become the oldest American to climb Everest, reported that he was among tourists preparing to set out when the avalanche happened.
"We've just heard from Ed. He is safe and sound at Base Camp," said the updated simply signed "Dan".
"Asha, a sherpa on Ed's team, has been lost in the avalanche," the update continued. "He was a member of the pioneering Sherpa group who went up to first camp to set ropes. He has a wife and two young children, ages one and three."
Overcrowding is a problem near the summit, where climbers wait their turn to scale or descend a steep rock formation called the Hillary Step, but Paudel of the Himalayan Guides said of the accident: "It had nothing to do with the overcrowding."
Authorities are installing two ropes - one to go up and one to come down - in an effort to ease congestion at the Hillary Step, located in Everest's "death zone" because of its thin air.
The climbing season usually ends in late May when rainy season winds and clouds push up from the south to cloak the Himalayas, making high altitude climbing virtually impossible. (Writing by Shyamantha Asokan; Editing by Douglas Busvine and Tom Heneghan)