Illegal fireworks were believed to have ignited fires that threatened homes and destroyed property in several locations, as well as caused an explosion at a block party that sent at least five people to the hospital, authorities across California said Sunday as they assessed damages and injuries from the July Fourth celebration.

In the city of Hollister, a man was arrested on suspicion of setting off a large mortar during a block party Saturday night. Once lit, the device fell over and shot projectiles into a crowd, hitting several people, police said.

A child was flown to a San Francisco Bay area hospital with severe injuries, several children suffered moderate to severe burns and one person had a possible broken leg.

"This incident is a grim reminder of the dangers of fireworks. Some of these children will be scarred for life," Hollister's police chief, David Westrick, said in a statement.

Shawn Gregory Bourdet, 35, told officers he was responsible for what happened and was arrested at the scene, the statement said.

Meanwhile, Los Angeles County sheriff's investigators suspect illegal fireworks sparked a fire that caused minor injuries to four firefighters and caused up to $3 million in damage to three warehouses.

They said witnesses reported seeing a group of young men shoot fireworks at mattresses outside one of the warehouses in an industrial area of South Los Angeles. The fire spread to the inside and several nearby buildings.

Fireworks debris was found at the scene, authorities said.

"They said it's a total loss," Daniela Avila, who works at a furniture company owned by her boyfriend, told KABC-TV.

"This is our second home, if anything our first home. We spent more time here than at our own home so this is hard," Avila said.

In Northern California, officials said fireworks may have started a wildfire that burned more than 320 acres and threatened homes in the city of Vacaville.

The fire started near a park Saturday night and embers were quickly spread by winds that gusted to 40 mph, said Mark Mazzaferro, a spokesman for the city between San Francisco and Sacramento.

"It's bone dry out there," Mazzaferro said. "Talk about a recipe for a big fire."

About 125 people left their homes in voluntary evacuations. Several homes were threatened, but no structures were burned, he said.

A crew of at least 130 firefighters worked throughout the night to battle the blaze. Witnesses reported seeing someone playing with fireworks in the park shortly before the fire began, Mazzaferro said.

Further north in the Rio Linda area of Sacramento, a grass fire threatened several homes, damaged five outbuildings and 10 cars and burned about six acres, the Sacramento Metro Fire District said.

One firefighter was hospitalized after suffering a muscular injury while battling the blaze.

KHTK-TV reports authorities confirmed Sunday that the fire was caused by fireworks.