Firefighters in northern California who have battled wildfires for nearly a week were bracing themselves for a rise in temperatures, higher winds and lightning that could spark new blazes on Sunday.

Crews made slow but hopeful progress in battling the blazes on Saturday, aided by good weather but hampered by smoky skies that grounded water-dropping aircraft for some of the day.

Reinforcements arrived to bolster overwhelmed crews and evacuation orders were lifted in some areas.

The changing weather brought fears of new fires overnight and warnings from state and local officials for residents in threatened areas to prepare to flee at any moment.

Firefighters hose down hot spots
Firefighters hose down hot spots in Boulder Creek (Marcio Jose Sanchez/AP/PA)

“There’s not a feeling of pure optimism, but a feeling of resolve, a feeling of we have resources backing us up,” Sonoma County Supervisor James Gore said.

Since August 15, state fire officials said more than 12,000 lightning strikes across the state have ignited more than 500 wildfires. Of those, about two dozen major fires were attracting most of the state’s resources.

Most of the damage was caused by three clusters of fire “complexes” that were ravaging forest and rural areas in and around the San Francisco Bay area. They have burned 1,120 square miles.

Among the casualties were ancient redwood trees at California’s oldest state park, Big Basin Redwoods, plus the park’s headquarters and campgrounds.

Overall, the fires have killed five people, torched nearly 700 homes and other structures and forced tens of thousands from their houses.

A firefighter monitors a controlled burn
A firefighter monitors a controlled burn in Boulder Creek (Marcio Jose Sanchez/AP/PA)

The changing weather brought good news for some communities, including Boulder Creek, an old logging community of about 5,000 people in the Santa Cruz mountains.

Fire officials said they expected the blaze to reach the community, but they took advantage of recent good weather to try to “herd” flames around the town.

The storms predicted for Sunday were expected to aid those efforts by changing the direction of the wind.

“As bad as that weather prediction is overall for certain parts of this fire, it actually is going to help us move it away from those certain communities,” said Mark Brunton, a battalion chief for the California Department of Forestry and Fire Protection, the state’s firefighting agency.

Responding to the emergency on Saturday, President Donald Trump issued a major disaster declaration to provide federal assistance.

Governor Gavin Newsom said in a statement that the declaration will help people in counties affected by the fires with crisis counselling, housing and other social services.