A polling place in Azusa, Calif., remained locked down Tuesday evening after a shooting that killed one person, officials said.

Police did not catch the shooter but said she was believed to be inside a nearby home. They said she was armed with an assault rifle, and that a man seen with her may be a second suspect. 

Two polling places were initially on lockdown. Officials gave an all-clear at Dalton Elementary School nearly three hours after the shooting, but kept the other polling place, Memorial Park, on lockdown. It was unclear whether the shooting had anything to do with the election.

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One adult was dead on arrival at a nearby hospital Tuesday, two were airlifted in critical condition and a fourth person was being treated, police said.

Azusa and Irwindale police officers exchanged fire with at least one suspect who darted into the nearby house, Azusa Police Chief Steve Hunt told reporters.

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Officers urged people in the area to shelter in place. “This is a very volatile and critical situation,” Azusa Police Officer Jerry Willison told the Los Angeles Times.

“Voters should avoid the area and, if necessary, cast a ballot at an alternate polling location,” L.A. County Registrar-Recorder/County Clerk Dean Logan said.

Willison said none of the officers involved in the shooting was hurt. He said they had to seek cover.

The shooting unfolded just outside Slauson Middle School and near Mountain View Elementary School, which officials locked down for part of the afternoon as well, Fox 11 reported.

Azusa is roughly 20 miles northeast of Los Angeles.

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The Associated Press contributed to this report.