Authorities say they found “suspicious devices” at a California retirement village where a resident is accused of killing a firefighter and wounding two other people after opening fire.

Long Beach Police Chief Robert Luna said 77-year-old Thomas Kim was arrested on suspicion of murder, attempted murder and arson on Tuesday after the shooting, which occurred when firefighters responded to a reported explosion.

Fire Captain Dave Rosa was killed, while another firefighter suffered non-life-threatening injuries and is expected to recover.

A third person was also struck by gunfire and was in a critical condition and undergoing surgery, Mr Luna said.

Firefighters responded to an alarm shortly before 4am on Monday local time at the 11-storey retirement facility in Long Beach, south of Los Angeles. They found windows blown out, activated sprinklers, a smell of gas and a fire that they extinguished, authorities said.

Firefighters were searching the building when shots were fired and the two firefighters were hit, Long Beach Fire Chief Michael DuRee said.

Mr Rosa, who had worked for the department for 17 years, died in hospital shortly after, Mr DuRee said. He is survived by a wife and two children.

Captain Dave Rosa had worked with the department for 17 years. Photo: LBFD

The other firefighter who was shot was not immediately identified and was in a stable condition in hospital.

Dozens of firefighters stood at attention and saluted as the flag-draped coffin carrying Mr Rosa’s body was brought out of hospital and loaded into a coroner’s van.

Community members waved American flags along the street outside the hospital as the procession of police and fire vehicles escorted the van to the coroner’s office.

Investigators were looking into whether the shooter intentionally lured first responders to the scene to ambush them, Mr Luna said.

“That’s the environment we work in today, as law enforcement and firefighters,” he said.

“You go to these scenes and you never know what’s on the other side of those doors. And these brave firefighters went through those doors and unfortunately they were met with gunfire.”

-with AAP