A tour bus has crashed into the back of a tractor-trailer on a Southern California highway, killing 13 people and injuring 31.
The bus was travelling on Interstate 10 when the crash occurred near Palm Springs, about 160 km east of Los Angeles, California Highway Patrol (CHP) Chief Jim Abele told reporters.
Mr Abele said because of the bus' speed, the truck's trailer pushed about 4 metres into the bus. The bus driver was among the 13 killed, he said.
"In almost 35 years I've never been to a crash where there's been 13 confirmed [deaths]," Mr Abele said. "So it's tough. It's tough for all of us."
Mr Abele said several survivors reported most of the passengers, all of whom were adults, were sleeping at the time of the crash.
Photographs from the scene showed the front of the tour bus wedged inside the back of the trailer, with emergency workers using metal ladders to reach the inside of the bus.
Mr Abele said the bus appeared to be ferrying casino-goers back to Los Angeles from the Red Earth Casino after a night of gambling.
Mr Abele said it was not immediately clear if alcohol, drugs or fatigue was a factor in the crash. He said it was not clear whether the bus was speeding, but said it was travelling "significantly faster" than the tractor-trailer.