AZUSA — One person was killed and three others were struck by gunfire Tuesday near a polling station in the Southern California town of Azusa, prompting authorities to lock down the polling place, a surrounding park and adjacent schools, officials said.

There was no indication that the incident about 25 miles (40 km) northeast of Los Angeles was related to Election Day, said Deputy Vincent Plair, a spokesman for the Los Angeles County Sheriff's Department.

But at least one of the victims was hit by gunfire on the way to the polling station to vote, the Los Angeles Times reported, citing a law enforcement source.

The circumstances of the shooting, and even the number of perpetrators, remained murky.

Police responding to a report of gunshots came under fire themselves and were initially pinned down as they arrived on the scene, according to accounts from Azusa police and the sheriff's department.

Officers returned fire, then surrounded a house where the shooting appeared to have originated, believing they had cornered at least one suspect, a woman carrying an assault rifle with "rapid-fire capability," inside the dwelling, Azusa Police Chief Steve Hunt told a news conference.

By then, three civilian victims - two female and one male - had already been struck by gunfire, one of them fatally, the chief said. 

Still a fourth individual whose condition and identity were unknown was left lying motionless - and presumably wounded during the exchange of gunfire - at the doorstep of the house, and might turn out to be the armed woman, Hunt said.

Officers keeping a safe distance on the perimeter of the property had yet to determine whether the person was a suspect or victim, the chief said.

Further complicating the situation, Hunt said, were reports of a possible second suspect, a man. Hunt said the motive behind the shooting remained unclear.

But the incident began around 2 p.m. local time (2200 GMT) as residents of Azusa, like Americans across the country, streamed to the polls to cast ballots in the U.S. presidential race between Democrat Hillary Clinton and Republican Donald Trump. 

The Los Angeles County Registrar and Recorder's office issued a Twitter advisory urging voters to avoid the area around two polling locations, one in Memorial Park and one in Dalton Elementary School, and to cast their ballots at alternate polling sites. 

Two other nearby schools, Slauson Middle School and Mountain View Elementary School, were also locked down, and then evacuated, Hunted said.

The Los Angeles Times said the person killed was a man in his 70s.

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