California Highway Patrol officers look over the bus involved in a crash with a tractor-trailer truck Thursday afternoon on a California freeway. The bus was carrying high school students on their way to a college visit. Ten people died in the fiery collision.

ORLAND, Calif. — A FedEx tractor-trailer crossed over a grassy median on a Northern California freeway and slammed into a bus carrying more than 40 high school students in an explosive crash that left 10 people dead, authorities said.

Among the students on the trip to visit Humboldt State University was Steven Clavijo, 18, a senior at West Ranch High in Santa Clarita, who planned to enroll in the school. Just as Clavijo was trying to catch a nap Thursday afternoon, he said he felt the big vehicle begin to shake from left to right and then he heard a loud boom.

“We knew we were in major trouble,” he said.

Both the bus and semi driver were among those killed in the fiery crash, authorities said. Many of those on the bus escaped through a window that someone had kicked open, Clavijo said, running for their lives to the other side of Interstate 5 before hearing an explosion and seeing the bus burst into flame.

Two more explosions soon followed, he said, and he and other survivors looked on knowing others were still trapped in an inferno.

Massive flames could be seen devouring both vehicles just after the crash, and clouds of smoke billowed into the sky until firefighters doused the fire, leaving behind scorched black hulks of metal. Bodies were draped in blankets inside the burned-out bus.

In addition to the drivers, three adult chaperones and five teenage students were killed in the crash, according to the California Highway Patrol. Their identities were not immediately released. The bus carried between 44 and 48 students, four chaperones and the driver, the patrol said.

EricWeiss, a spokesman for the National Transportation Safety Board, said a multi-disciplinary team of highway crash experts left on a flight Friday morning for the crash scene.

The crash happened a little after 5:30 p.m. on the interstate near Orland, a small city about 100 miles north of Sacramento.

The bus was one of two that the admissions office at Humboldt State University had chartered to bring prospective students from Southern California to tour the Arcata campus.

The bus was owned by Silverado Stages, a tour bus company based in San Luis Obispo. The company said in a statement on its website Thursday night that it was assisting authorities in gathering information. The students came from a number of Southern California high schools and a Humboldt spokesman said the college was working to confirm where exactly they were from.