Open this photo in gallery

       CalFire firefighters battle hot spots on the front of the Caldor Fire near Pacific, Calif., on Aug. 18, 2021. Many of the biggest blazes around California were still much less than 50 percent contained as of Friday morning.

       Max Whittaker/The New York Times News Service

       As another day of wildfire fighting began in California on Friday, fire crews were seeing a few glimmers of hope. Smoke from the Caldor fire raging southwest of Lake Tahoe had been helping to choke off the spread of flames, for instance, and the pace of evacuations was easing.

       But the state’s battle against summer wildfires is far from over.

       Town burns to ashes in raging Northern California wildfire

       California couple faces manslaughter charges for wildfire that started during gender reveal

       Many of the biggest blazes around California were still far less than 50 per cent contained as of Friday morning. Fire crews were stretched precariously thin. The air quality around Sacramento and San Francisco, battered by wildfire smoke, was expected to remain poor. And officials warned that it could be days or weeks before people evacuated from the Caldor fire were allowed back into their homes.

       That fire has grown to more than 68,000 acres since it began over the weekend, according to Cal Fire, the state’s fire fighting agency. It remained completely uncontained Thursday, even though more than 650 people were fighting it. The fire has destroyed more than 100 structures and still threatens about 7,000 others.

       More than 20,000 people in El Dorado County have been told to leave their homes or to prepare to do so, according to the governor’s office. A Cal Fire official, Dusty Martin, said at a community meeting Thursday that he expected mandatory evacuation orders for the Caldor fire to “last for a little while – at least a week, maybe upwards of two weeks.”

       The nearby Dixie fire, which has burned about 700,000 acres, an area about nine-tenths the size of Rhode Island, also remains a serious threat – even after burning for more than a month. As of Friday morning it was just over one-third contained and still threatened more than 16,000 structures. Three firefighters have been injured while working that blaze, and a local television station reported that 13 of them had tested positive for COVID-19.

       In Southern California, a new fire that started Wednesday in Kern County, north of Los Angeles, quickly consumed more than 3,000 acres and prompted fresh evacuation orders. That blaze, known as the French fire, was only 5 per cent contained Thursday.

       The California fires are among dozens that have been stretching emergency agencies across the western United States this month. Even though some fire crews have made significant progress in recent weeks, the prevailing weather conditions in many areas – low humidity, dry ground and high winds – are a recipe for further flames and destruction.

       The fire potential in most of California’s mountains and foothills is forecast to be higher than normal through September, and through October in areas prone to offshore winds, the National Interagency Fire Center said last week.

       The U.S. Forest Service said Thursday that it would close nine national forests in California to the public for two weeks, starting next week, to help protect residents and fire crews working in the area. Some of the backcountry around Lake Tahoe was also closed Thursday for at least a month.

       Story continues below advertisement

       A closure this week of the Eldorado national forest, where the Caldor fire has been burning, “was not taken very lightly,” said Jeff Marsolais, the forest supervisor there.

       “It was about trying to keep you out of the way from this spreading fire,” he said at the community meeting Thursday night. “It’s about evacuations, it’s about stretched resources and our inability to keep pace with the fire that was, at the time, growing 40,000 to 45,000 acres in a single burning period.”

       Our Morning Update and Evening Update newsletters are written by Globe editors, giving you a concise summary of the day’s most important headlines. Sign up today.