At least 12 Nepalese guides were killed and four remain missing after an avalanche on Mount Everest on Friday.

The guides had travelled ahead of group of climbers to set ropes when the avalanche struck at about 6:30 a.m. Four of the survivors were airlifted to a hospital in Katmandu, and several others are being treated at base camp.

From the Associated Press:

The avalanche hit an area nicknamed the "popcorn field" for its bulging chucks of ice and is just below Camp 2, Ang Tshering of the Nepal Mountaineering Association said. Camp 2 sits at an elevation of 6,400 meters (21,000 feet) on the 8,850-meter (29,035-foot) mountain.

One injured guide, Dawa Tashi, lay in the intensive care unit at Grande Hospital in the capital late Friday after being evacuated from the mountain. Doctors said he suffered several broken ribs and would be in the hospital for a few days.

Tashi told his visiting relatives that the Sherpa guides woke up early and were on their way to fix ropes to the higher camps but were delayed because of the unsteady path. Suddenly the avalanche fell on the group and buried many of them, according to Tashi's sister-in-law Dawa Yanju.

The disaster is the deadliest in the mountain's history. In 1996, eight climbers were killed during a snow storm, and in 1970, six guides died in an avalanche.

[Image via AP]