Five snowboarders have been killed in a backcountry avalanche in the US state of Colorado, local authorities said.

Clear Creek County Sheriff Don Krueger said in a statement that six snowboarders were caught in the slide on the area's Loveland Pass on Saturday. The condition of the lone survivor was not released.

The Colorado Department of Transportation closed a highway as many skiers were headed home from the nearby Arapahoe Basin ski resort.

Lisa Clarke Devore, who was headed back to Denver from the resort, told The Associated Press news agency that she saw a fire truck and ambulance on the pass, as well as two search dogs headed into the area of the slide.

She said she saw several ambulances, including one towing snowmobiles, driving toward the pass.

The pass, at an elevation of 3,655 metres, is popular among backcountry skiers and snowboarders.

On Thursday, a 38-year-old snowboarder died in an avalanche south of Vail Pass. Eagle County sheriff's officials said the man and another snowboarder likely triggered the slide after a friend on a snowmobile dropped them off at the top of Avalanche Bowl.

According to the Colorado Avalanche Information Center, ore than 18 people have died in avalanches this season nationwide.

US avalanche deaths climbed steeply around 1990 to an average of around 24 a year as new gear became available for backcountry travel.

Until then, avalanches rarely claimed more than a handful of lives each season in records going back to 1950.

Source: Agencies