The tour bus had crashed into the big rig’s trailer near Palm Springs, about 100 miles east of Los Angeles. Photos from the scene showed the front end of the bus had been demolished, Xinhua news agency reported.
Rescuers continued to search the wreckage for more victims. Throughout the morning, more bodies were removed from the bus and placed along the road.
The Desert Sun newspaper reported on its website that at least 25 bus passengers have been taken to local hospitals.
The big rig driver was unhurt.