California wildfires are spreading quickly, threatening hundreds of homes and forcing evacuations at a summer camp where flames temporarily trapped children.

Authorities have lifted an evacuation order for nearly 200,000 California residents who live below the crippled Oroville Dam that threatened to collapse and cause catastrophic flooding.

The water level has dropped behind the US's tallest dam, reducing the risk of a catastrophic spillway collapse and easing fears that prompted the evacuation of nearly 200,000 people downstream.

Evacuation orders affecting 188,000 people are in place until there is more information on the condition of the US's tallest dam's emergency overflow channel, a sheriff in California said.

Strong winds has seen the Oregon wildfire grow to nearly eight square miles, forcing evacuation of several homes.