Irwindale, California (CNN) -- A gunman killed at least two people and then himself Friday afternoon in a southern California office building, leaving police searching for more bodies in the aftermath, authorities said.
At least two other people had been shot, but their conditions weren't immediately known, said Capt. Michael Taylor of the Baldwin Park Police.
Authorities were checking for more victims in the building in Irwindale, Taylor added.
One victim died on the scene, and another died on the way to a hospital, Taylor said. The third dead person was the shooter.
The building is occupied by Southern California Edison, one of the nation's largest electric utilities, serving almost 14 million people, according to a company statement.
Employees from Southern California Edison were among the victims, but utility officials didn't provide further details, including whether the gunman was an employee.
"We can now confirm that SCE employees were victims in today's shooting," Ted Craver, chairman and CEO of Southern California Edison, said in a written statement. "This is one of the most horrible days in our company's history."
More than 200 employees work in the building, mostly in information technologies, utility spokesman Gil Alexander said.
"This is, of course, first and foremost a tragedy, and our thoughts and prayers go out to the families affected," Alexander said. "We're all anxious to find out what happened."
Two nearby schools, Walnut Elementary School and Olive Middle School in Irwindale, went into lockdown during the incident, said Laura LaTurno with the Baldwin Park superintendent's office.
CNN's Carey Bodenheimer and Sonya Hamasaki contributed to this report.