Emergency crews responded to the scene of an explosion resulting from an apparent industrial accident at a business called Quantum Energy Storage at 13350 Gregg St., near Scripps Poway Parkway in Poway, a sheriff's lieutenant said.
According a witness, the roof in the building collapsed in Poway after an explosion was heard around 12:50 p.m.
Brian Price works a half block from the damaged building when he heard the blast.
"Sounded like a jet was flying overhead and kicked in after burners," Price said. "People were pouring out of my office looking around to see if anything crashed. We didn't see any smoke or fire."
"Building doors were blown out and concrete was scattered everywhere. It looked like part of the roof caved in."
Four of the five people injured were taken to local hospitals. The fifth patient was treated at the scene. Officials said none of the injuries were life-threatening.
The company has yet to release a statement about the explosion.
Though the explosion was not believed to be criminal in nature, the sheriff's Bomb/Arson Unit was called in to investigate, officials said. A county hazardous-materials team also responded, testing the air and grounds and finding nothing toxic or unhealthy.
An investigation is underway to determine the cause of the explosion and whether or not the building is till structurally sound enough to continue to work in. The structure will remain off-limits to public until further notice, authorities said.