Five students, three chaperones and the drivers of the bus and FedEx truck were killed, according to the California Highway Patrol and Humboldt State University, which was to host the students' visit.
The tenth fatality was confirmed by a CHP spokeswoman yesterday as a chaperone on the tour bus.
"All of a sudden I heard people screaming," 17-year-old Jonathan Gutierrez told NBC's "Today" show, saying he had been asleep before the impact.
Gutierrez, who suffered cuts on his face, said the aisle of the tour bus filled with smoke and students broke windows to escape.
"It was a very surreal moment," he said.
More than 30 people were hurt after the driver of the FedEx truck lost control, jumped a divider on Interstate 5, side-swiped a car and smashed head-on into the bus Thursday evening, CHP spokeswoman Tracy Hoover said. "They are traumatized, absolutely," Hoover said of the injured.
"Most of them have scratches, cuts, burns, contusions and lacerations, a magnitude of injuries."
About 34 people were taken by air and land ambulances to area hospitals in varying conditions, police said.
No one in the car that was side-swiped was killed, though the driver was sent to hospital with unspecified injuries.
The highway was closed in both directions and was not expected to reopen until early Friday. Apart from the driver, the bus was carrying between 44 and 48 students and several chaperones to the university for a campus tour, CHP spokeswoman Lacey Heitman said.
The crash took place near the city of Orland, 95 miles (150 km) north of Sacramento, the state capital of California.
The students, traveling from Los Angeles area high schools, were part of a program Humboldt State said "brings low-income and first generation prospective college students from the Los Angeles and San Francisco areas to HSU's campus."
Pictures from the scene showed the bus reduced to a burned-out chassis resting sideways across the highway.
Yellow tarpaulins appeared to be draped over bodies in the wreckage.