Authorities say the accident happened on the southbound 15 Freeway near State Route 76 in the Fallbrook area at about 2:30 p.m.
Police say the bus skid out of control then overturned. They expect two lanes on the 15 freeway to be shut down for at least two hours.
This accident is not connected to another tour bus crash in corona that left 20 people injured this afternoon.
KABC-TV contributed to this report