Officials say they first got a report of a car explosion around 2:01 p.m. near 6th and Tehama. When emergency crews arrived, they found a FedEx truck that had signs of some kind of explosion.
Police are trying to determine whether the explosion came from a package in the back.
No injuries were reported but roads nearby are shut down and traffic is heavily impacted. Muni lines are being diverted.
(Stay with ABC7 News for the latest on this developing story.)