PALM SPRINGS, California (REUTERS) - A tour bus crashed into the back of a tractor-trailer on a Southern California highway before dawn on Sunday (Oct 23), killing at least 13 people and injuring 31, the authorities said.

The bus was travelling west on Interstate 10 when the crash occurred near Palm Springs, a city 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 15 feet (4.5m) into the bus. The bus driver was among the 13 killed, he said. The 31 injured passengers had minor to moderate injuries, Mr Abele said.

Mr Abele said the bus had been inspected by the CHP as recently as April and there was no indication of mechanical problems. 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.

The injured were being treated at hospitals while all westbound lanes of the interstate were closed near the crash, officials said. The bus had left the Red Earth Casino in Salton City, California, and was headed to Los Angeles when the crash was reported to the CHP at about 5.17am (8.17pm Singapore time), Mr Abele said.

The National Transportation Safety Board said it will investigate the crash and is sending an investigative team to the site.