LOS ANGELES, United States of America - Three people were killed in California when their helicopter crashed into a hillside after colliding with another chopper as the team battled a wildfire, emergency officials said early Monday.

The helicopters were dispatched to fight a fire that had erupted in brush in Cabazon, a town some 85 miles (137 kilometers) east of Los Angeles, on Sunday evening when they collided in mid-air, Cal Fire Southern Region chief David Fulcher told reporters.

One helicopter was able to land safely nearby.

"Unfortunately, the second helicopter crashed, and tragically all three members perished, which included one Cal Fire Division chief, one Cal Fire fire captain and one contract client pilot," Fulcher said.

He expressed condolences to the families of those who died, adding: "We have lost three great individuals."

Authorities said on social media that the fire had grown to about three acres (1.2 hectares) in Cabazon as firefighters responded.

A local ABC radio station affiliate described the helicopter that landed safely as a Sikorsky Skycrane, which can carry retardant that is dropped on flames, while the chopper that crashed was a Bell helicopter used for observation while battling blazes.

The National Transportation Safety Board has launched an investigation into the Cabazon accident, according to media reports.

The fatal incident comes 11 months after a Cal Fire helicopter crash-landed near Banning, just a few miles away, injuring three people.

California firefighters battle thousands of wildfires each year, with summer months particularly susceptible to blazes. An ongoing fire south of the city of Fresno has consumed 5,100 acres and is zero percent contained, Cal Fire reports.