Fire crews have fended off flames threatening Los Angeles' historic Mount Wilson Observatory, with smoke from unprecedented blazes across the western United States spreading as far away as Europe.
Dozens of fires have burned 1.8 million hectares in Oregon, California and Washington state since August, ravaging several small towns, destroying thousands of homes and killing at least 34 people.
The fires have thrust a debate about climate change to the forefront of the US election, with President Donald Trump downplaying the role a warming planet could have in the devastation during a visit to California.
His Democratic challenger Joe Biden is calling Trump a "climate arsonist" and says he is ignoring a "central crisis" facing the nation.
Fire officials say the Bobcat Fire burning northeast of Los Angeles since September is no longer an immediate threat to incinerate the Mount Wilson Observatory.
"I was telling people ... the defence of the Mount Wilson observatory was taking on the feel of a mini-Alamo," John Clearwater, public affairs officer for Angeles National Forest, said on Wednesday.
Twelve firefighting crews worked to protect the site and planes flew within 150m of it to fight the blaze.
"It would have been devastating if we had lost that observatory," he said.
But the blaze is still only at three per cent containment and behaving erratically, fire officials say, and authorities have ordered evacuations in the area.
The West Coast wildfires, which officials and scientists have described as unprecedented in scope and ferocity, have filled the region's skies with smoke and soot, compounding a public health crisis already posed by the coronavirus pandemic.
Scientists tracked the smoke as far away as Europe.
The European Union's Copernicus Atmosphere Monitoring Service is monitoring the scale and intensity of the fires and the transport of their smoke across the United States and beyond.
"The fact that these fires are emitting so much pollution into the atmosphere that we can still see thick smoke over 8,000 kilometres away reflects just how devastating they have been in their magnitude and duration," CAMS Senior Scientist Mark Parrington said.
The simultaneous burning of dozens of fires along the West Coast has stretched resources in the three states to their limit, particularly Oregon, where fires rarely impact the green Cascade Mountains in the way they have.
Trump on Tuesday night approved a request from Oregon's governor for a federal disaster declaration, bolstering federal assistance for the state.
Eight deaths have been confirmed during the past week in Oregon, with search teams still scouring incinerated towns for the missing.
The California Department of Forestry and Fire Protection said on Wednesday 17,000 firefighters were still battling 25 major fires and the state's death toll stood at 25.