UPDATE 5 p.m. Tuesday:
PECO spokeswoman Liz Williamson said PECO is seeking to reroute power to the estimated 4,000 customers dealing with power outages in Center City as they work to resolve the underlying problem.
"We are actively working to get power back to customers," Williamson said.
PECO still has not determined when power will be restored to customers.
Approximately 4,000 customers in the Center City area have lost electricity this afternoon, PECO confirmed.
PECO received reports at 3:18 p.m. today of problems with electricity in two areas, at 13th and Spruce streets and at 15th and Waverly Streets, according to PECO spokeswoman Liz Williamson
ABC reported that an underground transformer fire caused the problem. However, Williamson said the cause had not been determined at this time.
"We have crews responding to these issues and they're working to identify the issue," Williamson said.
Williamson said it is not clear yet when service will be fully restored.