A wildfire burning through Northern California became the state’s largest on record on Monday, scorching more than 290,000 acres, officials said.

The Mendocino Complex blaze — a conglomerate of the River and Ranch fires burning through rural Lake, Colusa and Mendocino counties — overtook last year’s Thomas Fire, which scorched more than 1,000 buildings and killed two people across 440 square miles in Ventura and Santa Barbara Counties.

The fire began on July 27 and was spurred on Monday by an ominous high-pressure system that brought hotter, drier and windier weather to the area, according to the California Department of Forestry and Fire Protection, or Cal Fire.

The fire has destroyed dozens of homes and other buildings, and more than 11,000 structures remained threatened, the department said.

The Mendocino Complex blaze reached 443 square miles, almost twice the size of Tucson, Arizona — which is about 226.7 square miles.

As of Tuesday, the Mendocino Complex blaze was only 30 percent contained. Firefighters expect the fire will be fully contained by Aug. 15.

Mandatory evacuations remained in effect across Mendocino, Lake and nearby Colusa counties, though some people were allowed to return home on Monday afternoon, Cal Fire said.

The fires have created such a haze of smoke in the Central Valley that Sacramento County health officials advised residents to avoid outdoor activities for the entire week.

Nearly 4,000 fire personnel, including 441 firefighters, were battling the wildfire.

It was unclear what caused the blaze, but the fire was one of more than a dozen burning amid record-setting heat waves in the drought-stricken state, according to Cal Fire.

Tens of thousands of residents across California have been displaced by wildfires this season, Gov. Jerry Brown told reporters Saturday.

California's record-breaking heat last month, with temperatures in the triple digits for days, helped fuel the wildfires, and they have been rekindled in August as temperatures again approach triple digits across the state.

Temperatures in parts of Northern California were expected to exceed 100 degrees on Tuesday, according to Weather.com. Colusa, California, where part of the Mendocino Fire Complex is burning, was also expected to reach 103 degrees, and the forecast for the rest of the month shows temperatures in the mid- to high-90s.

President Donald Trump declared a state of emergency in California on July 27, authorizing the Federal Emergency Management Agency to help firefighters to respond to the disaster areas.

More than 14,000 firefighters are now battling over a dozen major blazes throughout California, Cal Fire spokesman Scott McLean said.

A new fire erupted Monday in Orange County, south of Los Angeles, and prompted the evacuation of two canyons and some campgrounds as it expanded into the Cleveland National Forest. By nightfall, the fire had burned 4,000 acres of chaparral-covered hillsides and destroyed one building.