At least 12 people are dead and four are missing after what is being called the deadliest disaster to ever occur on the peak.

An avalanche swept down the mountain early on Friday, killing the group of Sherpa guides who were fixing ropes for the climbers.

“It took out many of the ladders, so this has now trapped over 100 climbers above the collapse, and also no one can climb below it,” climber Alan Arnette told CBS News. “So, basically, Everest has come to a complete stop at this point, and I’m sure many of the teams are reevaluating exactly how they want to move forward.”

Weather conditions have forced the search to come to a stop until at least Saturday; authorities say they have pulled twelve bodies from the snow so far, but there are some survivors. Those who escaped the avalanche said it came too quickly to move.

“It came out of nowhere, this huge block of ice that fell from above, flying right at us,” Dawa Tashi Sherpa said. “I wanted to run but there was no time, we were just trapped.”

The avalanche hit at an elevation of about 21,000 feet and is being classified as the deadliest disaster in the peak’s history; a blizzard was to blame for the last deadly incident, which killed eight climbers in 1996.

Over 300 people have lost their lives on the mountain since 1953, when the first climb was attempted.

Image via Wikimedia Commons