Update 6:25 a.m. EDT April 30: KNXV-TV reported early Friday that its crews have seen medical helicopters and an ambulance amid the massive law enforcement presence at the San Tan MotorPlex.

Heavy police activity also was reported at nearby Chandler Regional Medical Center, according to the news station.

Police still have not publicly released any information about the situation, but Pinal County Sheriff Mark Lamb said his office was one of the agencies involved, KNXV reported. Lamb told the station that no Pinal County deputies were hurt in the incident.

The other agencies at the scene, which include Gilbert police, Chandler police, the Maricopa County Sheriff's Office and the Arizona Department of Public Safety, have not said whether any of their officers were injured, according to KNXV.

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