San Diego, California - A shooting at a mosque complex in California killed three people Monday, with two suspected teenage gunmen later found dead in a car from self-inflicted gunshot wounds, police said.

Police said emergency response teams found the victims outside the sprawling Islamic Center of San Diego, before later finding the shooters, aged 19 and 17, also dead.

TV footage from a helicopter showed armed response teams gathered outside a building, with one unidentified person lying in a pool of blood.

Dozens of patrol cars were lined up around the Islamic Center, described on its website as the largest mosque in San Diego County, which lies in southern California.

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After a short period of lockdown when authorities advised residents to stay inside, San Diego police announced that the threat at the center had been "neutralized."

"We received a call of an active shooter at the Islamic center. Within four minutes, officers arrived on scene and observed immediately three deceased victims out in front," San Diego Police Chief Scott Wahl told reporters.

"We immediately began to deploy with an active shooter response into the mosque and adjacent school," he said, adding that police had received calls about more gunfire nearby, where a landscaper at work had been shot at but not hit.