Massive wildfires spread across thousands of acres in Southern California on Wednesday, destroying hundreds of homes and forcing thousands of residents to evacuate, with fierce winds expected overnight.

The National Weather Service has placed much of southwest California in its “critical risk zone” for fire weather, including Los Angeles, Long Beach, and Anaheim. It said “confidence has increased” that winds will restrengthen late Wednesday night into Thursday morning.

Wind and dry weather helped spark the fires, which began Monday night into Tuesday. The initial round of winds were up to 80 miles per hour.

The largest of the fires, known as the Thomas Fire, began in Ventura County, sprawling 65,000 acres by Wednesday morning, threatening 12,000 structures and forcing 27,000 people to evacuate, officials said. Dozens of schools have closed. There have been no reported deaths.

Gov. Jerry Brown declared a state of emergency as more than 1,000 personnel fought the fire, the Los Angeles Times reports, with the fire burning through oil fields before crossing a major freeway. Charlie Beck, the Los Angeles police chief, warned Wednesday the region was facing “a multiday event,” adding: “This will not be the only fire.”

President Trump on Wednesday expressed his concern for the Californians who have been affected by the fires.

"Our thoughts and prayers are with everyone in the path of California’s wildfires. I encourage everyone to heed the advice and orders of local and state officials. THANK YOU to all First Responders for your incredible work!" Trump tweeted Wednesday. The Federal Emergency Management Agency has approved assistance grants for the fires, to fund emergency services throughout the region.

The fire on Wednesday morning closed the 405 Freeway, a major commuting thoroughfare, as it reached the tony Bel Air section of Los Angeles.

It acted similarly to a wildfire that devastated Northern California in October, killing 20 people.

The year has been the costliest firefighting season on record, as fires have become larger, more frequent and more expensive, which many climate scientists say can be attributed partly to increasing dry conditions caused by climate change.

Fires now are also considered more dangerous because they are burning closer to homes and people as the West becomes more populated.