Two teenage gunman have opened fire at the Islamic ‌Centre of San Diego in California, killing three men outside the mosque.

Two suspects were later found dead, apparently from self-inflicted gunshot wounds.

All of the children who were attending a day school that is part of ‌the mosque ‌complex were accounted for and safe after ​the shooting, which erupted shortly before midday on Monday (local time), San Diego Police Chief Scott Wahl said.

Wahl said the FBI was called in to assist in investigating the incident, which he said was being treated as a hate crime.

Scores of ⁠law enforcement officers called to the Islamic centre ‌found ​the bodies of three men shot dead outside the building. One was a security guard ​who Wahl credited ‌with likely having helped prevent further bloodshed.

Soon after, police discovered the ​bodies of two teenage males, aged 17 and 19, in a vehicle in the middle of a street. They had died from apparently self-inflicted gunshot wounds, he said.

Wahl said ​investigators were still piecing together details of what ‌precipitated the shooting and how the violence transpired.

Shots were also fired at a landscaper a couple of blocks away in what apparently was a separate shooting incident, though police did not say whether a connection had been ruled out. The landscaper was not ​injured, Wahl said.

-AAP