Officials are responding to a fire in a drainage channel that goes under State Route 163, just north of Interstate 5 near Balboa Park.
San Diego Police say they have shut down the Robinson ramp to the 163 to prevent people from getting on the freeway. There are no other closures as of yet.
The on ramp reopened shortly after.
A command post has been set up on the 163 under the Laurel Street Bridge.
HAZMAT teams and CalTrans are responding.
