The slide occurred between 10 and 10:30 a.m. at Berthoud Pass on US 40, causing officials to close the highway.
Colorado Department of Transportation initially reported several cars were buried and pushed off the road, however after probing with poles, no cars were found buried on the roadway and two were found pushed off the road.
People in other cars not trapped in the slide immediately tried to help dig out people trapped in the two cars pushed off the road.
“Immediately a lot of people got out of the car, started grabbing shovels,” said witness Robert Aldor. “I saw skis, snowboards, trying to dig with whatever they could to get everything dug out."
About 15 minutes after the slide, rescue crews arrived and helped pull out all eight people trapped in the snow.
“It happened so fast,” said Aldor. “Instantly everybody got out and tried to do what they could do, to dig people out or do whatever they could to help.”
All eight survivors were transported to St. Anthony Central Hospital where they were checked out. One survivor was admitted overnight with moderate injuries, authorities say.
The avalanche was 100 feet wide and 15 feet deep, according to C-DOT.
Officials say they blasted the area, known as the Stanley slide area, as recently as a few days ago in an attempt to prevent an avalanche. However, they say recent snow mixed with high winds broke loose a giant 100-foot slab of snow.
"Our crews said it was the largest they have ever seen. It took three paths," said Stacey Stegman, spokeswoman for C-DOT.
Berthoud Pass, an 11,307 foot pass, is the main route to Winter Park, one of Colorado's largest ski areas and is located 60 miles west of Denver.
Officials have opened US 40 at Berthoud Pass, after clearing all of the snow debris from the road and finishing blasting maintenance to assure safety from other snow slides in the area.
(Copyright KUSA*TV, All rights reserved. The Associated Press contributed to this report.)