The Ontario Fire Department responded to the crash.
The jet was on a ramp while undergoing a routine engine run-up test when it jumped the chocks holding it and rolled into the hangar.
"Fortunately the incident did occur after hours, and a lot of the employees had already left," said Massiel De Guevara with the Chino Valley Fire District. "And the ones that were inside were able to self-evacuate prior to firefighter arrival."
Three maintenance workers were on the plane. They were treated by rescuers but refused to be hospitalized.
The plane narrowly missed workers who were inside the hangar.
"What they told me was they thought a bomb went off," said Robin Dill, a friend of the workers. "They were kind of dazed and confused at first, they weren't quite sure. You could hear it all the way at the other side of the airport."
The plane was not intended for flight.
The twin-engine aircraft is known as a Bombardier Aerospace Challenger 601. The business jet is registered to an Irvine company called Grady International.
The FAA will be called in to investigate the incident.