Azusa police told residents to “shelter in place” following a “critical incident” around Memorial Park North Recreation Center. Los Angeles County Fire spokeswoman Vanessa Lozano told TIME that officials were treating two injured patients after the incident about 2 p.m. One person was dead on arrival. Los Angeles County Fire Inspector Joey Marron said he did not know the conditions of the wounded.

Azusa Police Chief Steve Hunt said authorities believe a woman armed with an assault rifle is responsible for the violence. The suspect has not yet been apprehended after she allegedly exchanged gunfire with about six police officers and then fled into a residential home, Hunt said.

“The scene is still not stable,” the police chief said at a news conference. “This is an active situation.”

The shooting did not take place inside the polling place, Hunt said. It’s unclear what sparked the gunfire.

City officials urged voters to find alternative polling places due to an “active shooter situation.”

Dean Logan, the Los Angeles County registrar-recorder county clerk, initially said two polling places in Azusa are “currently impacted,” including the Memorial Park North Recreation Center and Dalton Elementary. Dalton has since reopened to voters.