A grizzly bear has attacked and killed a female cyclist who was camping in a small US town in western Montana.

The pre-dawn attack happened in Ovando, a town of fewer than 100 people about 100 kilometres north-west of Helena, according to Greg Lemon, from the Montana Fish Wildlife and Parks.

The bear had previously wandered into the area where the victim was camping and left but later returned, police said on Wednesday.

A team of law enforcement and wildlife specialists has been brought in to track down and kill the bear, officials say.

A crew aboard a helicopter was assisting as searchers looked for a “day bed” where the animal might be sleeping to get out of the heat, Mr Lemon said, adding the bear was believed to have left Ovando after the mauling.

The small, quiet town of Ovando stayed busy on Tuesday after a bear attack left one woman dead at a campground just inside the town, sending shockwaves through the community. https://t.co/udaUdo6KCo

— NBC Montana (@NBCMontana) July 7, 2021

Wildlife workers set five traps in and around Ovando in hopes of capturing the bear, Mr Lemon said.

An initial report said the victim had been riding a bicycle at the time of the attack. That was not the case, police said.

Mr Lemon said his understanding is that the victim was part of a group on a bike trip.

The victim’s identity was not immediately released and further circumstances surrounding the attack are under investigation.

“Our first concern is the community’s wellbeing. The next step is to find the bear,” Mr Lemon said.

Officials did not say exactly where the attack occurred, but police said there were other people camping in the vicinity of the attack.

Ovando saloon owner Tiffanie Zavarelli said it was the first fatal bear mauling that she knew of in the community, located along the Blackfoot River beneath a mountain range that rises into the remote Bob Marshall Wilderness, a large expanse of public forests.

An estimated 50,000 grizzlies once inhabited western North America from the Pacific Ocean to the Great Plains.

Hunting, commercial trapping and habitat loss had wiped out most by the early 1900s.

Grizzly bears have been protected as a threatened species in the US since 1975, leading to a slow recovery in a handful of areas.

-AAP