More than 30 people have been killed by wildfires that are sweeping through US West Coast states, officials say.

Dozens of people are missing in Oregon alone, with one emergency official saying the state should be preparing for a “mass fatality incident”.

Fires have been raging in Oregon, California and Washington for three weeks, burning millions of acres of land and destroying thousands of homes.

Tens of thousands of people have been forced to flee their homes.

Democratic presidential challenger Joe Biden warned on Saturday that “climate change poses an imminent, existential threat to our way of life” and accused President Donald Trump, a climate sceptic, of denying “that reality”.

Mr Trump, who is due to visit California on Monday to be briefed on the latest situation, blames the wildfires on poor forest management.

The fires have now scorched an area of land the size of New Jersey, officials say.

The smoke pollution from the wildfires has left Oregon’s largest city, Portland, with the worst air quality in the world, followed by San Francisco and Seattle, according to IQAir.com.

In Oregon, where firefighters are battling 16 large blazes, 40,000 people are under mandatory evacuation orders.

Oregon’s Office of Emergency Management (OEM) says the fires have killed 10 people, but officials warn the final death toll could be much higher.