DENVER — Five snowboarders were killed Saturday afternoon after apparently setting off an avalanche atop Colorado’s Loveland Pass, a popular spot for backcountry enthusiasts, a law-enforcement official said.

The official, Sheriff Don Krueger of Clear Creek County, a rural, mountainous area about 60 miles west of Denver, said that six snowboarders were ascending the pass together at around 2 p.m. when the slope broke away, releasing a deadly plume of snow 400 to 500 feet wide and 8 feet deep.

One of the snowboarders was able to extract himself, descend to a nearby highway and flag down a truck from the state’s Transportation Department. It took rescuers four hours to recover the bodies of the other five, whose names were not released Saturday.

Krueger said all of the snowboarders had been equipped with avalanche gear, including beacons designed to transmit their location through thick layers of snow.