2 helicopters battling a California brush fire collided mid-air, killing a pair of firefighters and a pilot

• Three people were killed when two helicopters battling a California blaze collided on Sunday. 
• The tragedy unfolded when crews were dispatched to a brush fire in Riverside County. 
• A Cal Fire division chief, a Cal Fire captain, and a pilot contracted by the department died. 

Two firefighters and a pilot were killed when the helicopter they were using to battle a southern California brush fire collided mid-air with another chopper that was also involved in efforts to put out the blaze, officials said. 

The tragedy unfolded Sunday at around 6 p.m. as crews were dispatched to a fire that erupted in the Riverside County community of Cabazon. 

"While engaged in the firefight, two helicopters collided," David Fulcher, a southern region chief for California's Department of Forestry and Fire Protection (Cal Fire), told reporters during a press conference. 

One helicopter managed to land "safely" nearby, but all three people aboard the other chopper — a Cal Fire division chief, a Cal Fire captain, and a pilot contracted by the department — were killed, according to Fulcher. 

The crash sparked an additional four-acre fire, which was later extinguished. 

"This was a tragic loss for the community, the fire service community and Cal Fire, and Riverside County Fire Department," Fulcher said. 

It was not immediately clear what caused the two choppers to collide. The National Transportation Safety Board is investigating the incident. 

Fulcher added that he was "thankful" that the disaster "wasn't worse."

"The individuals in the first helicopter were able to land safely without incident, and no one else was hurt," he said. 

The chief described the victims, whose identities were not immediately released, as "three great individuals" and "three fathers, three husbands, three friends, three sons."

Fire crews were responding to a fire that originated in a structure and quickly spread into the surrounding vegetation at the time of the collision. 

Both helicopters involved in the collision were "under exclusive agreement" with Cal Fire, Fulcher said.