National Transportation Safety Board investigators were en route to the site of a deadly bus crash east of Los Angeles Monday.
The California Highway Patrol says at least eight and as many as 10 people were killed and another 38 injured when the bus swerved for several minutes and crashed Sunday evening on Highway 38 near Mentone.
Highway 38 leads to Big Bear, a popular area that's home to a ski resort and other recreational locations.
The tour bus company, Scapadas Magicas, runs tours from Tijuana and is registered to an address in National City.
Passengers -- a victim's family members identified many as medical students from Tijuana, Mexico -- were returning from a skiing and snowboarding trip when the bus began swerving and the driver reported a problem with the brakes.
Gerardo Barrientos says the brakes failed and the driver called out for someone to call 911 but there was no cell reception.
Barrientos says there were bodies strewn everywhere and people screaming for help.
He was uninjured but his girlfriend suffered bruises and a hairline vertebra fracture, and another friend suffered a broken neck.
The bus collided with a Saturn sedan and Ford truck that was towing a trailer. Betty Harvey was traveling down Highway 38 when she saw the bus speed past.
"I saw a headlight in the rear-view mirror," said Harvey. "I moved over and he went flying past. He was swerving all the way down."
Passengers told NBC Los Angeles that the bus swerved for about three minutes before it flipped near Bryant Street.
The crash left the highway littered with body parts and debris, and the bus sideways across both lanes with its windows blown out, front end crushed and part of the roof peeled back like a tin can.
Crews worked through the night to recover the dead, but one body remained aboard the bus early Monday, said Rocky Shaw, a San Bernardino County coroner's investigator.
Officials hadn't been able to retrieve the body because the front end of the bus was dangling over the edge of the roadside.
Investigators were trying to pick up any personal property to help identify victims.
"Speed was probably a factor," said CHP Officer Mario Lopez. "We do not know if there was a mechanical failure or driver error. That's what investigators at the scene are going to determine."
Authorities plan to retrieve a passenger list from inside the bus Monday morning. The number of casualties might change during the investigation, Lopez said.
Highway 38 was expected to remain closed during the investigation Monday.
In National City, a sign for FedEx deliveries is the only indication of the company Scapadas Magicas.
An NBC 7 San Diego crew knocked on the door but no one answered.
The office building appears to be used mostly as a storage facility. No other tenants in the building knows anything about the tour bus company.
Federal transportation records show that the company is licensed to carry passengers for interstate travel. No crashes involving a company owned bus have been reported in the past two years, according to federal records.
However, in 22 inspections covering 2011 and 2012, the company was cited 59 times for safety violations according to those same records.
NBC 7 San Diego obtained the records that show the company's Vehicle Maintenance BASIC score of 75.2 exceeds the threshold for intervention by 10.2 points.
The score shows that 75 percent of buses in the same class have a safer record.
The tour operator, INTERBUS Tours, released a statement Monday on its Facebook page.
"INTERBUS Tours and its team are working to support our clients and their families that unfortunately suffered an accident coming down from the mountains of Big Bear in San Bernardino CA. Interbus staff are located in offices and in the hospitals where we know the authorities transferred the wounded."