SAN DIEGO — California Highway Patrol is seeking possible witnesses of a deadly crash Friday on Interstate 805.

The incident happened shortly after 9 a.m. when a pickup truck drove off the freeway, overturned and landed on the 43rd Street on-ramp to southbound Interstate 805.

According to CHP, a 75-year-old man was driving a Nissan truck in the southbound No. 4 lane of I-805, south of Division Street, while another driver was in the No. 3 lane in a commercial vehicle, which was described as a tow truck towing a mini excavator.

It is unknown if the two vehicles collided, but the commercial vehicle was reported to have been swaying back and forth, CHP Public Information Officer Samuel Mendoza said in a news release.

For reasons still under investigation, the driver of the Nissan lost control of the truck, prompting the vehicle to go down a dirt embankment, overturn and strike a light pole, CHP said. The truck ultimately landed on the 43rd Street on-ramp to southbound I-805.

According to CHP, both occupants of the Nissan were not wearing seatbelts at the time of the crash, causing them to be ejected from the vehicle. The 75-year-old driver was pronounced dead at the scene of the crash and the adult passenger was transported to Scripps Mercy Hospital with major injuries.

No further victim information was immediately available.

A be-on-the-lookout alert was issued by CHP for the commercial vehicle following the crash.

Officials were unable to locate the vehicle during a search of the surrounding area, Mendoza said. At this time there is no additional identifying information.

CHP has asked anyone who may have witnessed the incident or has video to contact Officer J. Rutherford at 858-293-6000.

The cause and circumstances that led to the crash are still under investigation by CHP. Drug or alcohol are not believed to have been a factor, according to officials.

The identity of the person who died on the crash has not yet been publicly released.