US authorities said on Sunday night that they have found a "deceased male" on Canfield Mountain in the northwestern US state of Idaho, the site of an earlier ambush by gunmen of firefighters tackling a blaze.

"This evening, members of the SWAT team located a deceased male on Canfield mountain," said a statement from Idaho's Kootenai County sheriff department, adding that "a firearm was found nearby."

The statement added that the shelter in place order -- which was enacted during a standoff between authorities and an unknown number of gunmen -- "is being lifted."

Two firefighters killed

Two people were killed when firefighters tackling a blaze were ambushed by an unknown number of gunmen in an ongoing standoff in the northwestern US state of Idaho on Sunday, the local sheriff said earlier.

"We now have two deaths. We have an unknown amount of casualties. We still have civilians that are coming off of that mountain... We are actively taking sniper fire as we speak," Sheriff Robert Norris told reporters.

He said the fire on the mountain in Kootenai County was still raging and vowed that law enforcement would "neutralise" the shooter "as quickly as possible".

Asking people to stay away from the area, Governor Brad Little said in a post on X, "This is a heinous direct assault on our brave firefighters. I ask all Idahoans to pray for them and their families as we wait to learn more."

Local news reports citing police scanners stated that multiple firefighters had been shot.

Kootenai County Sheriff's Lieutenant Jeff Howard told ABC News that firefighters were responding to a small brush fire that broke out in the Canfield Mountain nature area on the eastern side of the city when they came under gunfire from somebody in a nearby wooded area.

Howard said that officials were investigating whether the fire was deliberately set.