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Three people have died following a helicopter crash during a firefighting mission in the US state of California.

The incident happened on Sunday evening after fire crews were called to a blaze near Cabazon, Riverside County.

The two helicopters collided, with one then landing safely and the second crashing into the ground, killing everyone on board.

An investigation has been launched into the cause of the crash by the National Transportation Safety Board.

The victims were identified as a fire captain and division chief from the state's Department of Forestry and Fire Protection (Cal Fire), as well as a contracted pilot. They have not been named.

David Fulcher, southern region chief for Cal Fire, described the incident as a "tragic loss".

"We have lost three great individuals. Three fathers, three husbands, three friends, three sons," he said.

"Daughters have lost their fathers, sons have lost their fathers".

Mr Fulcher told a press conference the fire initially broke out in a building but later spread to surrounding vegetation.

The crash also caused an additional four-acre fire. All fires were eventually extinguished.

The helicopter that crashed was a Bell helicopter, which was being used for observation. The helicopter which landed safely was a Sikorsky Skycrane, which typically carries fire retardant or water. Both had been contracted to Cal Fire.

These are the first deaths of the 2023 fire season, according to .