Los Angeles - A delivery truck ploughed into a bus carrying American students in northern California, killing ten people and injuring at least 30, the California Highway Patrol said.

The bus was one of three bringing high school students to tour Humboldt State University on Thursday, which is about a six-hour drive north of San Francisco.

“My understanding is the FedEx truck crossed the highway divide, and it was a head on collision with our bus,” Joyce Lopes, a university official, told AFP. The other two buses arrived safely.

The university said the dead included the drivers of the two vehicles.

The identities of the other victims were not immediately released.

Images from the scene showed the highway was divided by a grassy median.

Photos of the bus showed a fire-gutted wreck, with the once-white metal exterior blackened and crumpled.

On the bus were low-income and first-generation prospective college students, travelling as part of a university-sponsored program to introduce them to the college and other prospective students.

“Students were transported to six different hospitals, because it was a fairly remote place ... where the accident occurred,” Lopes explained, adding it was taking time to track down each student.

Two bus passengers were in critical condition, said Enloe Medical Centre, which had received 11 of the injured passengers.

Four were in fair condition and five had been discharged, the statement added.

Another local hospital had discharged all five of the injured crash victims it had treated, according to the New York Times.

“The Humboldt State community sends our deepest condolences to all those involved in this tragic accident. We are saddened beyond words,” the university said in a statement.

“Our hearts go out to those who have been affected, and we are here to support them, and their families, in any way possible,” HSU president Rollin Richmond had said earlier.

The bus that crashed had travelled from Los Angeles, the university said.

The Los Angeles Unified School District said in a statement Thursday night it did not know how many of the district's students were involved in the crash.

Superintendent John Deasy said the district had provided support at the crash site and would also do so at district schools Friday morning.

The university is in Arcata, California, not far from the border with Oregon to the north and the crash happened in Orland, about 160 kilometres north of Sacramento, the state capital.

Sapa-AFP