(CNN) -- The death toll in a Southern California tour bus crash is expected to rise Monday as authorities try to get to bodies still inside the bus, authorities said.
At least eight people were killed in the Sunday crash.
"It's a horrific scene," California Highway Patrol spokesman Mario Lopez said. "Probably one of the worst ones I have seen in my career. There are victims inside the bus, outside the bus, personal belongings [everywhere]."
A coroner is trying to identify the victims' bodies.
The bus rear-ended a sedan in San Bernardino County, east of Los Angeles, around 6:30 p.m. local time. The crash happened in a mountainous area of State Route 38, between Mentone and Forest Falls, San Bernardino Fire Department spokesman Eric Sherwin said.
At least 42 people were injured. Some injuries were minor, and some were severe, he said. The National Transportation Safety Board has sent a team to investigate.
The top of the bus over the driver's seat was caved in, and part of the roof was ripped open. The bus driver is being questioned, Lopez said.
A parade of ambulances snaked down a narrow, sloping highway Sunday night. The highway was reduced to one lane for both inbound and outbound ambulances, which had to contend with a downhill grade and winding roads.
The cause of the crash is unclear.
Witnesses said that they saw smoke coming from the back of the bus and that it was going very fast, said Michelle Profant, a spokeswoman for the California Department of Transportation.
"I heard that the driver, when interviewed by the CHP, indicated that he had problems with his brakes, but nothing has been proven so far," she said.
The tour company is Scapadas Magicas of National City, California, Lopez said. The company did not immediately return a request for comment early Monday.
Federal safety records indicate Scapadas Magicas had no reported crashes in the past two-year reporting period. The company received a "satisfactory" rating in a safety review last month.