One woman was killed and three other people were injured when an explosion ripped through the first floor of a California office building on Tuesday afternoon, forcing evacuations and prompting a large response from emergency workers.

Carrie Braun, a spokeswoman for the Orange County Sheriff’s Department, called the blast suspicious but would not comment further about what specifically had caused it.

The authorities, she said late Tuesday, were “still trying to determine whether the explosion was accidental or intentional.”

Just after 1 p.m. Tuesday, firefighters were called to the two-story office building at 11 Mareblu in Aliso Viejo, Calif., a city about 50 miles south of Los Angeles, said Capt. Tony Bommarito of the Orange County Fire Authority.