It happened in the 2000 block of Walnut Street in the Rittenhouse Square section of the city.
PECO crews were working there when they found a large void opening underneath the street.
The streets and water departments were called to the scene.
The water department conducted a test, concluding the void was caused by a possible sewer leak.
Workers will put a plate over the hole and the street should reopen Wednesday night. A more permanent fix should be completed on Thursday.
