Nearly two dozen wildfires in California have forced thousands to flee their homes and have lead to the burning of large swathes of land.
More than 9,000 firefighters are battling to contain the fires.
The crews are working to dampen 21 blazes, according to an update from California's forest fire department late Monday night, with new outbreaks reported since Monday.
The biggest fire, the Rocky Fire, prompted evacuations as it swept through Colusa, Lake and Yolo counties north of Sacramento, the state's capital.
More than 13,000 people have been forced to flee homes threatened by Rocky, CALFIRE spokeswoman Alisha Herring said.
Only 12 percent under control, Rocky has burned through more than 62,000 acres (25,000 hectares), destroying 50 structures, about half of them homes.
"It's the Rocky Fire that continues to really be a fast-moving fire that definitely continues to challenge us today," CALFIRE spokesman Daniel Berlant said on CNN.
He said the fire ripped through the forests at break-neck speed, with firefighters struggling to keep apace.
"Over the weekend, 20,000 acres burned in just about a five-hour period. That's an unprecedented historical rate of spread," he said.
In an update Monday night, CALFIRE said the threat of new fires being ignited by lightning from passing thunderstorms remains high.
"Storms will be on the dry side so a high risk has been issued for dry lightning through tonight," the department said.
The National Weather Service issued a red flag warning for northern California, cautioning that "extreme fire conditions are occurring or imminent."
A total of some 142,000 acres of land have burned so far, according to figures provided by the state.
Weather in the drought-stricken state was the main culprit, with several thousand dry lightning strikes reported over the weekend.
"The drought is playing a huge role. With four years of dry conditions, our vegetation, the trees, the brush, are tinder dry," Berlant said.
California is in the throes of a record-breaking drought, with much of the state completely parched and residents asked to make major cutbacks in water use.
The northern part of the state is the worst-hit by fires, where forests were completely engulfed by the infernos, and several stretches of highway were forced closed.
In areas where fires had been put out, charred cars were all that was left behind on some roads, and trees were left smoldering on the blackened earth.
But Berlant said firefighters were making headway on some fronts, with at least three fires extinguished since the weekend and others almost under control.
"We are making progress on several fronts. In fact several of the fires are near containment or almost completely contained," he said on CNN.
A state of emergency was issued Friday, and the California National Guard has been called in, underlining the scale of the threat facing the western state.
A firefighter from South Dakota, Dave Ruhl, 38, was killed Thursday while fighting the Frog Fire in the Modoc National Forest outside Alturas.