California’s largest wildfire so far this year continued to grow as it chewed through timber in very hot and dry weather.

The Park Fire has scorched more than 660 square miles since erupting on July 24 near the Sacramento Valley city of Chico and burning northward up the western flank of the Sierra Nevada.

Containment remains at 34%, Cal Fire said.

The conflagration’s early explosive growth quickly made it California’s fourth-largest wildfire on record before favourable weather reduced its intensity late last week.

It reawakened this week due to the heat and very low relative humidity levels.

A large portion of the burned area was in the mop-up stage but spot fires are a continuing problem, officials said on Thursday.

The fire’s north-east corner was the top firefighting priority, operations deputy Jed Gaines said.

“It’s not time to celebrate,” he said. “We got several more days of hard work to hold what we got in there.”

The latest Park Fire assessments found 636 structures destroyed and 49 damaged.

A local man was arrested after authorities alleged he started the fire by pushing a burning car into a gully in a wilderness park outside Chico.

About 100 miles to the south, a new forest fire in El Dorado County was exhibiting extreme behaviour, and some Park Fire aircraft were being diverted there.

The Crozier Fire, about 10 miles north of Placerville, had burned more than two square miles of timber and chaparral as of Thursday evening and was just 5% contained.

The fire threatens 1,625 structures, according to Cal Fire.