Officials in a Northern California community canceled an annual Fourth of July fireworks celebration as an estimated 26,000 residents remained displaced by a growing wildfire, while hundreds of firefighters toiled under extreme heat to keep flames from reaching more homes.

The Thompson fire broke out before noon Tuesday about 70 miles north of Sacramento, near the city of Oroville in Butte County. It sent up a huge plume of smoke that could be seen from space as it grew to more than 5.5 square miles.

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Oroville Mayor David Pittman said there was a “significant drop in the fire activity” Wednesday, and he was hopeful that some residents could soon be allowed to return home.

The fire’s progress was stopped along the southern edge, and firefighters working in steep terrain were trying to build containment lines on the northern side. By Wednesday evening, containment stood at 7%.

“On that north side they have some real struggles in terms of the topography,” Pittman said.

More than a dozen other blazes, most of them small, were active across the state, according to the California Department of Forestry and Fire Protection, or Cal Fire. A new fire Wednesday afternoon prompted brief evacuations in heavily populated Simi Valley, about 40 miles northwest of downtown Los Angeles.

California’s largest blaze, the Basin Fire, covered nearly 22 square miles of the Sierra National Forest in eastern Fresno County and was 26% contained.

In Oroville, a state of emergency was declared Tuesday night and evacuation centers were set up. The evacuation zone expanded Wednesday into foothills and rural areas beyond the city of about 20,000 people.

With July Fourth in mind, authorities warned that fireworks are banned in many places, including most of Butte County. Authorities also cited the ongoing evacuations and damage caused by the Thompson fire for the cancellation of Oroville’s fireworks show, which had been specially permitted.

California State Parks officials said in a statement that many agencies have a large number of resources responding to the blaze and are working to get everyone back home as quickly as possible.

“These agencies also have employees with families displaced by these evacuations who are tirelessly assisting the community of Lake Oroville,” the statement read.

Authorities warned of full legal consequences for any illegal use of fireworks.

“Don’t be an idiot, cause a fire and create more problems for us,” Butte County Sheriff Kory L. Honea said. “No one in the community is going to want that.”

There was no immediate official report on property losses. An Associated Press photographer saw fire burn three adjacent suburban-style homes in Oroville.

The fire ignited sprigs of grass poking from the concrete edges of Lake Oroville as gusty winds whipped up American flags lining a bend of the state’s second largest reservoir and the nation’s tallest dam.

Residents standing on hillsides watched the orange glow as aircraft made water drops. A crew of more than a dozen firefighters saved one home as goats and other farm animals fled.

The cause of the blaze was being investigated. Red flag warnings for critical fire weather conditions were in effect when it erupted.

“The conditions out there that are in our county this summer are much different than we’ve experienced the last two summers,” said Garrett Sjolund, Butte County unit chief for Cal Fire, during a briefing. “The fuels are very dense, brush is dry. And as you can see, any wind will move a fire out very quickly.”

The conditions led the utility Pacific Gas & Electric to shut off power in some parts Northern California to prevent fires from being ignited by downed or damaged wires.

In Southern California, Joshua Tree National Park officials closed Covington Flats — an area with most of the park’s important Joshua tree populations — on Wednesday because of extreme fire risk after spring rains led to abundant grass that has now dried.

— The Associated Press