A 38-year-old man has been killed by a grizzly bear after he surprised the animal whilst riding his bike on a trail near Montana national park.

Law enforcement officer Brad Treat was killed in the Halfmoon Lakes area of the Flathead National Forest, just outside Glacier National Park.

The US Forest Service worker was cycling with another person when they surprised the bear, which knocked him off his bike.

The second rider left to look for help and was not injured. Authorities are looking for the bear.

Before Wednesday's attack there had been just 10 bear-related deaths in Glacier since the park was created in 1910.