A firefighter has perished in a blaze that was ignited two weeks at a gender-reveal party, the US Forest Service reported on Friday, as welcomed thundershowers brought some relief to weary fire crews in western Oregon.

The firefighter’s death on Thursday in the San Bernardino National Forest east of Los Angeles raised the death toll to at least 35 in the catastrophic spate of wildfires raging across the western United States in recent weeks.

Twenty-six of those victims have died in California,including two other firefighters – a Forest Service contractor killed in a lightning-sparked fire in northern California, and a private helicopter pilot whose chopper crashed on a water-dropping mission in Fresno County last month.

Authorities withheld the identity of the latest firefighter fatality pending notification of next of kin.

No details on the circumstances were immediately released except that the death occurred during the El Dorado Fire, which investigators have determined was triggered by pyrotechnics during a gender-reveal celebration on September 5.

That blaze has since charred more than 21 000 acres (8 500 hectares) and was 66% contained as of Friday, authorities said.

Twelve firefighters have suffered minor injuries and at least 10 structures have been destroyed by that fire.

Scores of wildfires have blackened some 3.2 million acres (1.3 million hectares in California since mid-August and another 1.7 million acres (650 000 hectares) in Oregon and Washington state since Labour Day.

The blazes, described by scientists and officials as unprecedented in scope and magnitude, have largely incinerated several small towns and destroyed thousands of dwellings in all three states.

The fires, many sparked by intense lightning storms, were stoked early on by record-breaking heat, drought-parched vegetation and bouts of howling winds.

Civilians account for the remaining 23 confirmed fire-related deaths in California since mid-August, as well as the eight in Oregon and one in Washington state. Thousands of evacuees, particularly in Oregon, remained huddled in emergency shelters, mobile trailers and hotel rooms.

Communities in Oregon, unaccustomed to wildfires of such magnitude and lacking sufficient resources to deal with them,was especially hard hit.

Emergency management officials have warned the death toll there could climb as search teams scour the ruins of homes engulfed in flames during chaotic evacuations early in the disaster.

Thundershowers brought drenching rains to the western slopes of the Cascade Mountains late Thursday and through Friday, helping a force of more than 6 000 firefighters make further headway against 10 major blazes still burning in Oregon.

The heavy rains also prompted flood and landslide warnings in areas where fire has stripped hillsides and canyons of vegetation.

Cooler, more favorable weather in the region since last week has already dispelled some of the smoky, polluted air and tempered the flames, enabling ground teams with axes and bulldozers to take the offensive while also allowing greater use of water-dropping helicopters and airplane tankers.

Higher humidity levels were likewise bolstering hopes for subduing blazes in the greater San Francisco Bay area.

“Milder weather is helping the fire fight as crews continue to gain ground on many of the major incidents,” the California Department of Forestry and Fire Protection said on Friday.

A key sign of success in the three states’ efforts to control the fires has been a steady rise in containment, a measure of the buffer lines that firefighters carve around the perimeter of each blaze by hacking away unburned vegetation to prevent its spread.