Emergency crews and investigators were working with the property’s owner and monitoring the area using drones to find the individuals, said the California Department of Forestry and Fire Protection.
It was not immediately clear if those missing worked at the warehouse or lived nearby.
People were urged to avoid the area after the Tuesday night blast, which set off a barrage of fireworks and caused a huge blaze that led to other spot fires and collapsed the building near Esparto in Yolo County about 64km north-west of Sacramento.
The cause of the explosion was under investigation.
“The fire will take time to cool, and once it does, explosive experts must safely enter the site to assess and secure the area,” the Yolo County Sheriff’s Office said in a statement.
The fire was held at nearly 80 acres as of Wednesday morning local time after scorching surrounding agricultural fields, officials said.
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The property is owned by “an active pyrotechnic license holder,” Cal Fire said in a statement.
“This type of incident is very rare, as facilities like this are required to not only follow our stringent California pyrotechnic requirements, but also federal explosive storage requirements.”
“The State Fire Marshal has sent an arson and bomb investigation team, and stands ready to provide additional support as needed,” the governor’s office said on the social site X.
Officials in nearby Sutter and Yuba counties announced that they were exploring alternatives for Fourth of July celebrations after their fireworks were destroyed in the blast.
