A man armed with a rifle started a wildfire and then began shooting at first responders in a northern Idaho mountain community, killing two firefighters and wounding a third during a barrage of gunfire over several hours, authorities say.

A shelter-in-place order was lifted Sunday night after a tactical response team used cell phone data to “hone in” on a wooded area where they found the suspect's body with a firearm nearby as flames rapidly approached, Kootenai County Sheriff Bob Norris said.

Officials did not release his name, nor did they say what kind of gun was found.

“We do believe that the suspect started the fire, and we do believe that it was an ambush and it was intentional,” Norris said. “These firefighters did not have a chance.”

Sheriff's officials said crews responded to a fire at Canfield Mountain just north of Coeur d’Alene around 1:30 pm, and gunshots were reported about a half hour later.

Investigators said the gunman acted alone.

“We believe that was the only shooter that was on that mountain at that time,” Norris said.

Three victims were brought to Kootenai Health, said hospital spokesperson Kim Anderson. Two were dead on arrival and the third was being treated for injuries, Anderson said. The wounded firefighter’s condition wasn’t known.

'We believe the suspect started the fire' - Kootenai County Sheriff Bob Norris. - KXLY, KREM via AP

The scene was sheer pandemonium as the brush fire burned and firefighters rushed to the scene only to come under heavy fire.

First responders made urgent calls for help on their radios: “Everybody’s shot up here ... send law enforcement now,” according to one dispatch.

Norris said it appeared the sniper was hiding in the rugged terrain and using a high-powered rifle. He said he instructed deputies to fire back.

“I’m hoping that somebody has a clear shot and is able to neutralise, because they’re not at this point in time showing any evidence of wanting to surrender,” the sheriff said.

An alert by the Kootenai County Emergency Management Office asked people to avoid the area around Canfield Mountain Trailhead and Nettleton Gulch Road, about 4 miles (6.5km) north of downtown Coeur d’Alene.

Though the shelter-in-place order was lifted, the sheriff’s office cautioned residents to be prepared because the fire was still burning.

Law enforcement is investigating whether the fire could have been intentionally set in order to lure first responders to the scene, Kootenai County Sheriff's Lieutenant Jeff Howard told ABC News.

The names of the slain and injured firefighters have not been released.

Nor has the name of the suspect, whose identity authorities are waiting to confirm, Norris said.

A procession of fire and law enforcement vehicles accompanied the bodies of the fallen firefighters as they were taken from the hospital in Coeur d'Alene to the medical examiner's office in Spokane, Washington, a neighbouring city just across the state line.

Fire trucks and firefighters waiting for a memorial procession for two firefighters who were killed in the ambush. - Heidi via Reuters

Department of Homeland Security Secretary Kristi Noem has been briefed on the Idaho shooting, ABC News reported.

Firefighters received the first call of a fire around 1:21pm local time, Norris said, and about 40 minutes later, reports emerged that they were being shot at.

"This is a heinous direct assault on our brave firefighters," Idaho Governor Brad Little said online. "I ask all Idahoans to pray for them and their families as we wait to learn more."

Faced with more than 17,000 square feet (1,580 square meters) of containment area, part of it burning, authorities used cell phone data to narrow their search. They identified a cell signal around 3:15 p.m. and noticed it had not changed location for some time, Norris said.

A tactical response team went to the location and found a deceased man with a weapon nearby. Officials believe the man was the shooter, the sheriff said.

The fire was burning close to the body of the suspect, and so authorities had to “scoop the body up” before it was engulfed in flames, Norris said.

Crews were stationed around the area overnight and the sheriff said the investigation would continue Monday morning.

Norris said investigators believe that once they are able to fully search the area, they may find that more weapons had been placed by the suspect.

The FBI has responded to the scene with technical teams and tactical support, Deputy Director Dan Bongino said.

“It remains an active, and very dangerous scene,” he wrote in a post online.

Coeur d'Alene is a city of 55,000 residents near the border with Washington.

Smoke rises in the Canfield Mountain area outside Coeur d’Alene, Idaho. – Reuters