LOS ANGELES (CNS) - The FedEx big rig involved in the fatal bus crash that killed 10 people, including five Los Angeles-area students, on Interstate 5 in Northern California was on fire when it crossed the median strip, witnesses to the collision told NBC4.  

The witnesses were a Washington state couple in a Nissan Altima, one of the three vehicles involved in the collision, the station reported on its website.  

The unidentified couple said flames were coming from the surface of the big rig as it crossed the 60-foot median strip and came at them.  

The couple, and the Silverado Stages tour bus carrying the students were both northbound.

The California Highway Patrol had previously said the big rig, which was towing two trailers, had crossed the median, struck a white vehicle and then collided with the bus, causing both to explode into flames. 

NBC4 said the role of the Nissan Altima in the collision was not clear. 

Families and friends of those killed in the crash were struggling to  cope with the tragedy today as authorities worked to positively identify the  victims and determine the cause of the fiery collision.

Counselors were dispatched to Los AngelesUnifiedSchool District  campuses and other schools across the area and officials warned that  identifying the people killed in Thursday night's crash on Interstate 5 near  Orland between the tour bus and a FedEx big rig will likely have to be done  using dental and medical records, and potentially DNA, delaying the process.  They also said it could be months before the cause of the wreck is known.

Five students were among the dead. The adults killed in the crash were  the bus driver, the truck driver and the three chaperones accompanying Los  Angeles-area high school seniors, according to the California Highway Patrol.  

One chaperone was identified as Arthur Arzola, 26, of Rancho Cucamonga,  who was a college recruiter. El MonteHigh School senior Adrian Castro was also  killed. Castro was a football player at the school.  

His mother, Veronica Soriano, told the Los Angeles Times she drove all  night to the crash site after she was unable to get information about her son  and was told this morning that authorities were 90 percent sure Castro was  killed.

“They just had to get the dental records to confirm,” she told the  newspaper.  

A 17-year-old girl, Marisa Serrato, who attended NorteVistaHigh School  in Riverside, was among those killed, her family told NBC4. Her twin sister,  Marisol, made the trip on a different bus and was not injured.   

Two other victims were identified as Mattison Haywood and her fiance,  Michael Myvett, 29. Myvett was a therapist for autistic children at a facility  in Torrance, and the couple got engaged in Paris on Christmas Day, according to  various media reports.

During a briefing at the CHP's Willows Area office, officials said 31  people had been taken to seven hospitals following the crash. Nine people died  at the scene, and one person who suffered severe burns died at a hospital.

The students were scheduled to visit HumboldtStateUniversity in Arcata  when their bus, which was chartered by the university, collided with the big  rig around 5:30 p.m. Thursday. The students had been accepted or were  considering attending the university.

The 48 occupants of the bus included 44 students, according to the Los  AngelesUnifiedSchool District.

According to the LAUSD, there were 19 students aboard the bus from 11  LAUSD schools -- Grant, Dorsey, Fremont, Visual Arts and Humanities (one of the  Robert F. Kennedy Community Schools), Manual Arts, Banning, Carson, Chavez,  Wilson, Chatsworth and MiddleCollege.

The university issued a list of all schools represented on the bus, and  posted it on the website www.humboldt.edu/emergency. The campuses included  schools in San Diego, Riverside and Orange counties.

A hotline for LAUSD parents concerned about students involved in last  night's bus crash has been established at (213) 241-3841.

A Long Beach Unified School District official said two of its students  were aboard the bus, and they suffered injuries described as “non-life- threatening.” The PasadenaUnifiedSchool District said four students from  that district took part in the bus trip, but only one was aboard the bus that  crashed. That student suffered leg injuries.

A PacificaHigh School senior will need surgery but is “expected to  make a full and complete recovery,” said Amy Stevens of the Garden Grove  UnifiedSchool District. His parents were with him today at a hospital, she  added. Santa AnaUnifiedSchool District officials said two students from that  district were on the bus and suffered non-life-threatening injuries.

Investigators said they would work to determine if any mechanical  failures contributed to the wreck, and would also review weather and road  conditions at the time. They said it was unclear if the driver of the FedEx  truck may have fallen asleep, or if there was a mechanical problem with the  truck, or if another accident may have occurred that forced the truck across  the freeway median.

Jonathan Gutierrez, a Banning High student who was aboard the bus,  tweeted that he had sustained “bruised leg, eyebrow cut open, scratches all  over my arm & all my stuff that I packed is burned. i'm beyond thankful that  I'm still here.”

Joyce Lopes, the HumboldtState vice president for administrative  affairs, said the university had chartered three buses for the campus tour. One  was for students from Fresno. The other two carried students from the Los  Angeles.  

Lopes said the students had been assigned to buses “largely, but not  entirely” on an alphabetical basis. Some students with names earlier in the  alphabet had left Los Angeles on the second bus, she said, adding that the  buses had been due to arrive at the university around 7 p.m. Thursday.  

The second bus from Los Angeles arrived safely, and counselors were made  available for the students, Lopes said.

A CHP spokeswoman said the collision sequence began with the big rig  crossing into the northbound lanes for an unknown reason, side-swiping a white  sedan and then colliding with the bus. This was followed by an “immediate  explosion,” she said.

The bus was owned by Silverado Stages of San Luis Obispo. A statement on  the company's website said it was helping authorities gather information  regarding the accident.

“Our top priority is making sure the injured are being cared for,” the  statement said.

Investigators from the National Transportation Safety Board were at the site.

HumboldtStateUniversity said the prospective students were en route to  a spring preview day scheduled for today -- part of a two-day visit to the Arcata campus.

The students were participants in the university-funded Preview Plus program, which brings low-income and first-generation prospective students from the Los Angeles and San Francisco areas to the campus, according to Humboldt  State.

Families of students who may have been affected were advised to contact university police at (707) 826-6327 for further information or guidance. The Red Cross has established a support site in Orland for victims of the crash at  the Orland Veterans Memorial Hall.