Avalanche leads to deadliest accident on Mount Everest

CNN/Larry Lazo

CNN/Larry Lazo

KATHMANDU, Nepal - Today was the single deadliest accident on Mount Everest.

An avalanche swept down a slope killing at least 12 Sherpa guides, seriously injuring three other guides, and four still remain missing.

A group of about 50 people, mostly Nepali Sherpas, were hit by the avalanche just below what is known as Camp Two, which is above 20,000 feet.

The guides had gone up early in the morning to fix the ropes for the hundreds of climbers gearing up for their final attempt to scale the 29,000 foot peak when the avalanche struck.

No climbers were killed or injured.