Two firefighters and a pilot have reportedly been killed after a mid-air collision involving two helicopters tackling a fire in California.

Emergency officials said the aircrafts were fighting a blaze in Riverside County, in the south of the US state.

Cal Fire Southern Region Chief David Fulcher said fire crews had been attending a building fire in the community of Cabazon which had extended into the vegetation around it.

A full wildland fire dispatch was initiated, which included fixed-wing and rotary-wing aircraft, and this is when the collision happened.

Sheriff’s deputies responded to the air emergency in the area of Pipeline Road and Apache trail at 7.20pm, according to a post by the Riverside County Sheriff’s office on X, formerly known as Twitter.

“Unfortunately, the second helicopter crashed and tragically all three members perished which included one Cal Fire Division chief, one Cal Fire captain and one contract client pilot,” Chief Fulcher said during a news conference early on Monday.

Chief Fulcher did not identify the victims.

The other helicopter landed safely and no one on board was hurt but the crash caused an additional 4-acre (1.6-hectare) fire, which was extinguished.

The helicopter which crashed was performing work under contract with the California Department of Forestry and Fire Protection, fire captain and spokesman Richard Cordova said.

The incident is being investigated by the National Transportation Safety Board.