A fifth victim, a female, was shot and taken to a hospital, as was the suspect, police Lt. Jennifer Amat said. Both were in critical condition.
Police said officers arrived at an active shooting scene at about 5:30 p.m.
“Our officers did engage in an officer-involved shooting,” she said. The suspect, who has not been publicly identified, suffered a gunshot wound. Amat said it was not known whether it was self-inflicted. No officers were injured.
A gun was recovered, she said, without providing further details about it.
Police said that they were working to determine a motive and that the investigation would include multiple agencies.
The building appeared to have several offices. The name of the business where the shooting occurred was not disclosed. Amat said that there are an upstairs, a downstairs and a courtyard area.
“It is a situation that was moving from different areas, so it’s my understanding it’s throughout that area,” she said.
Gov. Gavin Newsom, who called the events “horrifying and heartbreaking,” said in a statement that “our hearts are with the families impacted by this terrible tragedy tonight.”
Rep. Katie Porter, D-Calif., said she was monitoring developments.
“I’m deeply saddened by reports of a mass shooting in Orange County, and I’m continuing to keep victims and their loved ones in my thoughts as we continue to learn more,” she said in a statement. “My team and I will continue to monitor the situation closely.”
The nation is already mourning recent mass shootings in Colorado and the Atlanta area. Ten people died last week when a gunman opened fire at a Boulder, Colorado, grocery store.
A week earlier, eight people, including six women of Asian descent, were killed in three Atlanta-area spas.