Two enormous wildfires are believed to have merged into a 50-mile-long line of flame advancing through paper-dry forest in eastern Arizona.

US investigators have concluded that the Forest Service employee accused of starting the biggest fire in Colorado’s history did so deliberately, it was reported today.

A wildfire raging east of Los Angeles overran two fire engine crews, burning three people and shutting down the main road between Southern California and Las Vegas.

A US Forest Service ranger credited with reporting a fire that has blackened nearly 103,000 acres has been charged with starting the blaze.

US federal authorities have arrested a longtime US Forest Service employee for allegedly starting the largest fire in Colorado's history.