Three people are dead after two firefighting helicopters collided in mid-air Sunday night during an attempt to extinguish a brush fire in Riverside County, California.

The collision happened around 7:20 p.m. local time as crews were working to extinguish a fire on 20 acres of Native American land near Cabazon, the Riverside County Sheriff's Office said on social media.

The crash took place in the area of Pipeline Road and Apache Trail. The pilot and two crew members onboard were killed when the chopper crashed into a hillside.

The second helicopter made a hard landing but no serious injuries were reported, according to KABC.

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The helicopter involved in the crash was a contracted chopper for the California Department of Forestry and Fire Protection. The three crew members killed were described as a contract pilot, a department division chief and a department captain.

"I would like to express our deepest sympathies and sorrow to the family and coworkers of the personnel," California Department of Forestry and Fire Protection southern region chief David Fulcher said. "This was a tragic loss for the fire service community and Cal Fire and Riverside County Fire Department."

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A witness told FOX 11 LA they observed the helicopters collide before the crash.

California Department of Forestry and Fire Protection fire captain and spokesman Richard Cordova told the outlet that the Federal Aviation Administration and National Transportation Safety Board are investigating the collision.

This is a developing story. Check back for updates.