WASHINGTON, Sept. 10 (Reuters) - Dozens of extreme wind-driven wildfires burned through forests and towns in US West Coast states on Thursday (Sep 10), destroying hundreds of homes and killing at least nine people, authorities said.

Over the past 48 hours, four people died from fires in California, while four were killed in Oregon and a 1-year-old boy died in Washington state, police reported. Thousands faced evacuation orders in the three states.

The number of people under evacuation orders in Oregon alone climbed late in the day to some 500,000, about an eighth of the state's total population, a spokeswoman for the state Office of Emergency Management said.

Thousands more were displaced north and south in the neighboring states of Washington and California.

Oregon has borne the brunt of nearly 100 major wildfires raging across the western United States this week. Around 3,000 firefighters have been battling nearly three dozen blazes in Oregon, and fire officials saying about twice as many personnel are needed to bring those conflagrations under control.

Police have opened a criminal investigation into at least one Oregon blaze, the Almeda Fire that started in Ashland near the border with California, Ashland Police Chief Tighe O'Meara said.

O'Meara said investigators were treating the origins of the Almeda fire as suspicious.

"We have good reason to believe that there was a human element to it. so we're going to pursue it as a criminal investigation until we have reason to believe that it was otherwise," he told Reuters.

O'Meara said he expected the death toll from the Almeda Fire, initially blamed for two of Oregon's fatalities, to rise as search teams combed through the ruins of dwellings that burned in the midst of a chaotic evacuation.

Police in Medford as well as in Douglas County to the north cautioned against rumours left-wing anti-fascists and right-wing Proud Boy arsonists were starting the fires.

The Oregon blazes tore through at least five communities in the Cascade mountain range as well as areas of coastal rainforest normally spared from wildfires. In eastern Washington state a fire destroyed most of the farming town of Malden.

In central Oregon search and rescue teams entered torched communities like Detroit where firefighters led residents on a dramatic mountain escape after military helicopters were unable to evacuate the town.

A 12-year-old boy was found dead with his dog inside a burned car and his grandmother was believed to have succumbed after flames engulfed an area near Lyons, about 80km south of Portland, the Marion County Sheriff's Office said.