The explosion happened in the first floor of a two-story office building, said Capt. The person who died was inside the building when the blast occurred.
Orange County Sheriff's Cmdr.
The injured were taken to a hospital and there's no immediate word on their conditions.
The explosion at the office building in Aliso Viejo - about 50 miles (80.5 kilometers) south of Los Angeles - blew siding off the walls, exposing insulation and framing.
Bomb technicians from the Orange County Sheriff's Department, the Federal Bureau of Investigation and other agencies were investigating, said Paul Delacourt, the assistant director in charge of the FBI's field office in Los Angeles.
"As far as what I'm hearing there was no vehicle involved", Carrie Braun of the Orange County Sheriff's Department said.
"We have confirmed there was no vehicle inside", Bommarito said, adding there was an explosion inside the building.
Authorities have not yet found explosive devices in the area, according to officials.
Orange County Fire Authority Chief Brian Fennessy said children at a daycare across the street were not injured. The other woman was burned and her head was bleeding.
Bomb squad investigators and FBI agents are looking into what caused the blast but authorities said there was no lingering threat, according to NBC. Dave Sawyer says authorities haven't determined whether the explosion was accidental or intentional. The cause of the blast is being investigated.
Fire and sheriff's officials said the building appeared to be undergoing some type of renovation.
It wasn't immediately clear how many people were hurt, but authorities said there were at least two patients transported.