At least 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, the local sheriff said.

The blaze was still raging on the mountainside in Kootenai County as law enforcement exchanged gunfire with the shooter or shooters, Sheriff Robert Norris told reporters.

“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,” he said at a press conference.

The firefighters were battling a blaze when they were ambushed by gunmen in the US state of Idaho. Photo / Intel Tower via X

The shooter showed “no evidence of wanting to surrender”, he continued, adding: “As soon as somebody has a clear shot, I encourage them to take that shot to neutralise the threat.”

He said authorities believed the two people who were killed were firemen.

Earlier, local fire chief Pat Riley described himself as “heartbroken” by the attack.

He told local TV station KHQ that no evacuations had been ordered, even though the fire was still burning.

Norris and other officials told residents to shelter in place until the standoff was over.

Serious gun violence is common across the United States, where many states have few barriers to the purchasing of firearms.

According to the Gun Violence Archive, there have been 189 mass shootings in the United States this year – defined by the organisation as incidents where at least four people are killed or wounded, other than the shooter.

– Agence France-Presse