US President Donald Trump attends a briefing on wildfires in McClellan Park, California on Monday. Photo: VCG

US President Donald Trump on Monday suggested global warming will reverse itself and dismissed climate change as a cause of ferocious fires engulfing swaths of the US West, during a briefing in California on the deadly blazes.

Trump, who flew into Sacramento on the third day of a reelection campaign swing, pushed back against state officials arguing that a heating climate underlies the ever-stronger blazes, which have killed at least 35 people since the start of summer and forced hundreds of thousands of people out of their homes.

"I wish science agreed with you," responded Wade Crowfoot, head of the California Natural Resources Agency, to which Trump replied: "I don't think science knows, actually."

Trump on his arrival also repeated his argument that the wildfires are due to poor maintenance of forest areas, making them more combustible.

"There has to be strong forest management," he said.

"With regard to the forests, when trees fall down after a short period of time, about 18 months, they become very dry. They become really like a match stick," he added. "They just explode."

Minutes earlier, Democratic challenger Joe Biden assailed Trump from the opposite coast as a "climate arsonist" whose reelection would be catastrophic for the environment.

"If you give a climate arsonist four more years in the White House, why would anyone be surprised if we have more of America ablaze?" Biden said, savaging Trump for failing to "take responsibility" for the ongoing wildfire crisis.

"We need a president who respects science, who understands that the damage from climate change is already here," added Biden, who was speaking in Delaware.

Climate change amplifies droughts, which dry out regions, creating ideal conditions for wildfires to spread out-of-control and inflict unprecedented damage.

The blazes across California, Oregon and Washington State have burned more than 5 million acres with fears the death toll may rise.

AFP