Firefighters battle the Pickett Fire burning in the Aetna Springs area of Napa County, Calif., on Saturday. (AP Photo/Noah Berger)

Thousands of homes were under evacuation orders and warnings on Sunday from wildfires in Northern California wine country and central Oregon as crews battled the flames in dry, hot weather.

The Pickett Fire, which had charred about 10 square miles of Napa County, was just 11% contained on Sunday, according to the California Department of Forestry & Fire Protection, or Cal Fire.

Some 190 people were ordered to leave their homes, while another 360 were under evacuation warnings as the fire threatened 500 structures near Aetna Springs and Pope Valley, about 80 miles north of San Francisco, said Cal Fire spokesperson Jason Clay.

In Oregon, the Flat Fire in Deschutes and Jefferson counties had grown to almost 34 square miles, with about 4,000 homes under various levels of evacuation notice, including 1,000 with orders to leave immediately, according to the state Fire Marshal’s Office.

Firefighters were able to cut containment lines and continued to suppress fires in some residential areas. However, they faced significant challenges Sunday with difficult terrain, low humidity and triple-digit temperatures in some areas, officials said.

Some homes have burned, and officials said they were working to confirm the status of structures.

More than 1,230 firefighters backed by 10 helicopters were battling the California fire, which began in a remote area on Thursday after a week of hot weather. The cause of the fire is under investigation.

Residents of the Western United States have been sweltering in a heat wave that hospitalized some people, with temperatures hitting dangerous levels throughout the weekend in Washington, Oregon, Southern California, Nevada and Arizona.

Although it’s difficult to directly tie a single fire or weather event directly to climate change, scientists say human-caused warming from burning fossil fuels like coal and gas is causing more intense heat waves and droughts, which in turn set the stage for more destructive wildfires.