Kathmandu, Nepal - A high-altitude avalanche Friday killed 12 Sherpa guides and seriously wounded three in the single deadliest accident on Mount Everest, officials said.

Four others are missing, said Madhu Sudan Burlakoti of Nepal’s Tourism Ministry, adding that six people were injured in total. A group of about 50 people, mostly Nepali Sherpas, were hit by the avalanche at more than 20,000 feet, said Tilak Ram Pandey of the ministry’s mountaineering department.

The avalanche took place just above base camp in the Khumbu Ice Fall.

So far rescue workers have pulled out 12 bodies from under mounds of snow and ice but are still searching for the three missing guides. Two Sherpas who were injured were taken by helicopter to hospitals in Nepal’s capital, Katmandu. Ang Tshering of the Nepal Mountaineering Association said the area where the avalanche hit is nicknamed the “popcorn field” and is just below Camp 2 at 6,400 meters (21,000 feet).

Before Friday, the deadliest single-day toll was from an accident in May 1996, when eight climbers disappeared when a huge storm hit. Their tragic story was chronicled in Jon Krakauer’s bestselling book “Into Thin Air.”