Thick flames engulfed a large bus on the shoulder of State Route 163, sending heavy smoke into the air for miles during rush hour.
The fire broke out just past 5 p.m. on Wednesday near the Kearny Villa Road exit in San Diego's Miramar neighborhood, California Highway Patrol (CHP) officials said.
Live video from the NBC 7 chopper showed the flames consuming the MTS bus. Traffic was snarled for miles as crews fought the blaze.
Officials said there were no passengers on board; the driver was able to escape safely.
No other information was immediately available.