Several people missing after fire, explosion level California fireworks facility

Seven people were missing after a fire and powerful explosion levelled a commercial fireworks facility in rural northern California, authorities said on Wednesday.

Aerial footage from local news media showed the large, warehouse-like building blown to pieces Tuesday evening in an enormous, thundering fireball that rocked a wide area around the Yolo County community of Esparto, about 64 kilometres west of Sacramento, the state capital.

The blast, belching out a pall of thick, black smoke, was followed by dozens of smaller explosions flashing in the sky over the site, apparently ignited by the inventory of pyrotechnics stored at the location.

Flames spread from the explosion charred about 32 hectares of surrounding vegetation, according to Jason Clay, a spokesperson for the California Department of Forestry and Fire Protection.

Two people injured in the initial event received medical treatment, and seven other individuals were missing, Curtis Lawrence, chief of the Esparto Fire Protection District, told reporters at a briefing on Wednesday, about 24 hours later.

The cause of the incident, which occurred three days before the July Fourth U.S. Independence Day celebrations that typically involve fireworks displays, was under investigation by the state fire marshal's office, Lawrence said.

Authorities said firefighters and other emergency response personnel were keeping a safe distance from the site as teams continued to make assessments of ongoing risks posed by live fireworks, which continued to go off at random intervals through Wednesday evening.

Teams were flying drones and aircraft over the area seeking to determine the fate of the missing and to monitor lingering hazards, according to Lawrence.

Authorities declined to say whether the missing were workers from the facility or bystanders, but he said there were no casualties among firefighters or other emergency personnel.

"I can say I have not seen anything like this," Lawrence said.

Asked how authorities would know when it was safe enough to venture further into the site, he said, "It's tough to get a definitive answer of when that's going to be and what that actually looks like."

An evacuation zone was established around the site, and about 150 homes and farms were without power as a result of the incident, Lawrence said.

He described the demolished facility as a licensed pyrotechnics business involving commercial fireworks sold for public display. But it was unclear whether fireworks were merely stored there or also produced on site.