Some of the largest wildfires ever in the Western U.S. state of California continued to rage Saturday, charring 1 million acres (4,046 square kilometers) in one week.

President Donald Trump issued a major disaster declaration Saturday, which will provide federal assistance. California's Gov. Gavin Newsom said the aid will help with crisis counseling, housing and other social services in counties where people were affected by the fire.

Two clusters of wildfires, the LNU and the SCU fire complexes, in the San Francisco Bay Area became the second- and third-largest wildfires by size in recent state history.

While cooler, more humid nighttime weather helped fire crews make headway, the daytime forecast of warm, dry weather, erratic wind gusts and lightning could undo much of that progress, state fire officials said.

The National Weather Service issued a red flag warning of high fire danger for the area where the worst fires are burning - across the Bay Area and along the Central Coast, beginning Sunday morning until Monday afternoon.

"The worst is not behind us. We are in a battle rhythm," California Department of Forestry and Fire Protection Chief Thom Porter tweeted.

In one week, the state has responded to more than 585 fires, mostly small and sparked by some of the thousands of lightning strikes. Most of the damage was inflicted by three groups of fires that torched forest and rural areas in the San Francisco Bay Area and nearby wine growing area.

Wildfires across the state have killed at least five people and injured 43 others, including firefighters, and burned nearly 700 homes and other structures. About 175,000 people have been told to evacuate.

On Friday, Newsom sought international aid, asking Canada and Australia for resources and support as nearly 14,000 firefighters from California and 10 other U.S. states battle the fires with the help of the National Guard and U.S. military.

Newsom said the fires have "disproportionally impacted" northern California, where tens of thousands of people have been forced to flee their homes and hundreds of homes and other buildings have been destroyed.

"We simply haven't seen anything like this in many, many years," Newsom said. "These fires are stretching our resources, our personnel."