Three people have been killed in a shooting at a mosque in San Diego, California, which officials believe was perpetrated by two teenage attackers.

The attack took place on Monday morning as officers were investigating a call about a possibly suicidal teen who had run away from home.

Police were alerted to the shooting at the Islamic Center of San Diego and found three victims who had been shot in the front of the building.

Shortly afterwards, they received another call that shots had been fired nearby from a vehicle at a landscaper. Officers found the suspects - aged 17 and 18 - dead from self-inflicted wounds in a vehicle not far from the mosque.

Among the deceased victims was a security guard who worked at the centre and heroically prevented more casualties.

The incident is being investigated as a hate crime by the FBI, due to writings found by the mother of one suspect.

Police were first called to the mosque at 11:43 local time and observed what appeared to be three deceased individuals out front, as explained by San Diego Police Chief Scott Wahl.

There were no officers involved in firing weapons, and no sign of any active shooter.

About two hours before the attack, the mother of one of the suspects had reported that her son had left home with several of her guns. Comments from the police suggested that the suspect's behaviors were inconsistent with those of a suicidal individual.

A note left by the suspect contained generalized hate rhetoric but no specific threat to the mosque.

Children were present at the scene as it unfolded, with the Islamic Center also housing the Al Rashid School, which provides religious and language education, leading nearby schools to go on lockdown.

Imam Taha Hassane condemned the violent act, emphasizing that places of worship should not be the scene of violence. California Governor Gavin Newsom stated he was horrified by the attack, asserting that such acts of terror against communities of faith would not be tolerated.

The investigation is ongoing as officials seek to gather more information about the motives behind this tragic incident.