A billboard toppled over early Tuesday and part of it was resting on top of a high-voltage transformer near Imperial Beach.
A metal post holding up the billboard collapsed at 2 a.m. along Palm Avenue, west of Interstate 5. The nearest cross street is Thermal Avenue.
San Diego Police and San Diego Fire-Rescue crews arrived to find the billboard resting on top of the transformer controlled by San Diego Gas & Electric.
The board, which was posted on private property belonging to American Recycling, landed on city property.
SDFD officials say a metal post holding up the board was rusted and broke at the bottom where it connects to the asphalt.
No one was in the area where the billboard fell, firefighters said.
SDG&E crews were on the scene and were going to shut down power to the transformer.
Crews from the company that owns the billboard, arrived to the area as of 7 a.m. They were awaiting the arrival of a crane from San Bernardino County to help remove the sign.