The bus was traveling from El Monte to San Ysidro when the driver swerved on a rain-slicked highway and lost control. The bus went over an embankment, ejecting some of the passengers before it landed on its roof.
Officials say there were no seat belts on the bus.
News video from the scene showed the bus upside down on a grassy embankment near the southbound side of the 15 Freeway. Traffic was backed up for miles in the immediate aftermath of the crash.
#FreewayIC (Final): We had 21 total patients. 18 have been transported. We are brokenhearted to report we have 3 deceased on scene. We would like to thank our automatic partners for your assistance on this call. @CALFIRESANDIEGO, @OFA3736, @Vistafire, Pala Fire, and MCP FD.— North County Fire (@NorthCountyFire) February 22, 2020
"We are brokenhearted to report we have 3 deceased on scene," the Fire Department said in a statement.
Additional details about the victims were not immediately available.
The bus company, Executive Lines, has an office in El Monte, but the staff did not make any comments.