A grizzly bear has mauled a mountain biker to death in a national park in the US.

The attack took place a mile away from a campground in the western part of the Glacier National Park in Montana.

The victim has been named by Montana authorities as US Forest Officer Brad Treat, 38.

He was cycling in the Half Moon Lakes area of the Flathead National Forest with an unnamed friend when they apparently surprised the bear.

According to Flathead County Sheriff Chuck Curry, Mr Treat was ripped from his saddle by the bear while his uninjured friend rode off to find help.

His body was found an hour after emergency services were called and was declared dead at the scene.

The area has been closed to the public which is around 3 miles from the park's west entrance.

Glacier National Park (AP)

Armed officers are searching for the bear responsible but have yet to find it.

Before this incident there have only been 10 bear-related human deaths in Glacier Park since 1910.

Lion, bear and tiger live together Show all 7 1 /7 Lion, bear and tiger live together Lion, bear and tiger live together Leo, Baloo and Shere Khan - "brothers" since cubs Noah's Ark Animal Sanctuary Lion, bear and tiger live together Leo watching Shere Khan wade through their enclosure's creek Noah's Ark Animal Sanctuary Lion, bear and tiger live together Leo and Shere Khan Noah's Ark Animal Sanctuary Lion, bear and tiger live together The BLT (Leo, Baloo and Shere Khan) while still cubs Noah's Ark Animal Sanctuary Lion, bear and tiger live together Baloo licking Shere Khan's nose Noah's Ark Animal Sanctuary Lion, bear and tiger live together Baloo nuzzling his "brother" Shere Khan Noah's Ark Animal Sanctuary Lion, bear and tiger live together (From left) Shere Khan, Leo and Baloo on the verandah of their enclosure den Noah's Ark Animal Sanctuary

Glacier officials say there are usually one or two non-lethal encounters between bears and humans each year inside the park.