Authorities are working to account for those affected after a massive explosion rocked a fireworks facility in Northern California on Tuesday evening.

A violent blast rocked a fireworks facility in Yolo County, California, on July 1, injuring two people and leaving seven others unaccounted for.

According to Fox News, the explosion occurred just before 6 p.m. in the small town of Esparto, triggering a large-scale emergency response that forced firefighters to retreat due to extreme hazards.

Firefighters initially entered the building to search for victims but quickly withdrew after assessing the extent of the destruction. Esparto Fire Chief Curtis Lawrence said the conditions inside were too hazardous to continue, citing “the severity and the risks that were there” during a news conference on Wednesday, July 2.

Since the explosion, emergency crews have avoided reentering the building. Instead, they have used aerial drones to scan the large debris field for any signs of the missing individuals. Officials have not confirmed whether the missing people worked at the facility, but no firefighters suffered injuries in the blast.

Investigators have not yet determined the cause of the explosion. Leading the inquiry, the Office of the State Fire Marshal deployed an arson and bomb team to the site.

The California Department of Forestry and Fire Protection (CAL FIRE) confirmed the building belonged to a licensed pyrotechnics operator, though authorities have not released the owner’s name.

The blast knocked out power for hundreds of residents, and officials have kept access to the surrounding area restricted. As of Wednesday afternoon, only a few fire units remained at the scene, down from more than 30 that initially responded.

Lawrence said conditions remain too dangerous to allow crews back inside. “This is obviously an incident of great magnitude,” he said. He added that his team is working to reduce the exclusion zone and safely restore power to the community.