It happened under a street construction project around 8:30 a.m. on Tuesday.
Eyewitness News reporter Josh Einiger just happened to be at the scene at the time and described the explosion as "extremely loud and startling."
The force of the blast sent metal plates briefly airborne. A few minutes after the incident, black smoke started pouring out of the ground under the plates.
A contractor on that job said he thought it was a transformer, but that is still under investigation.
No one was injured.