The San Diego Union-Tribune reports the accident occurred shortly after 4:30 p.m. Thursday.
A witness told the California Highway Patrol the crash was triggered by a wrong-way driver speeding in the northbound carpool lane of Interstate 805 near Interstate 5 in the Sorrento Valley area.
CHP Officer Mary Bailey says nearly a dozen cars were involved and several caught fire.
A witness who called 911 reported the whole northbound side of the freeway was on fire.
CHP Officer Jake Sanchez says three people were killed. He says a fourth person was badly hurt but is expected to survive.
Authorities closed all of the freeway’s northbound lanes, snarling traffic.