Large amounts of smoke were seen coming from the commercial bus heading north on I-5 just north of state Route 52 at 8:25 p.m., California Highway Patrol reported.
All of the passengers, including children, evacuated the bus without injuries. San Diego Fire-Rescue Departments extinguished the fire within minutes.
CHP said the fire was confined to the engine compartment.
The bus was owned by Americano Busline, according to a highway patrolman.
Traffic along I-5 was slowed due to the thick smoke coming from the bus.