Investigators suspect illegal fireworks sparked a fire that injured four firefighters and caused up to $3 million in damage to three warehouses in South Los Angeles.

Los Angeles County Sheriff's officials said witnesses reported seeing a group of young men shooting fireworks at mattresses outside one of the warehouses in the Florence area Saturday night. The blaze spread to two other warehouses.

Four firefighters suffered minor injuries. Fireworks debris was found at the scene.

In Northern California, officials said illegal fireworks may have started a wildfire that burned more than 320 acres and threatened homes in the city of Vacaville, and a grass fire in the Rio Linda area of Sacramento that damaged five outbuildings and 10 cars. One firefighter was hospitalized after suffering a muscular injury in the process.