The lights went out just before 3 p.m., NBC Washington reported.
Potomac Electric Power Company said a problem at one of its substations caused the outages in the northwestern parts of the city.
“An issue at Pepco’s Florida Avenue substation has impacted service to approximately 39,000 customers in the District of Columbia. We are working to restore service to customers as quickly and safely as possible and are investigating the cause of this incident,” Pepco tweeted at 3:25 p.m. ET.
Among the neighborhoods affected were Adams Morgan, Shaw, and Mt. Pleasant. The city fire department was said to be inundated with emergency calls, including reports of people stuck in elevators.
No serious injuries were initially reported.
Washington, and other parts of the East Coast, are in the middle of a heat wave. The lights went out in the nation’s capital on Monday, July 15 as well.
That outage came just two days after a massive blackout in New York City that affected more than 70,000 customers, and left landmarks without electricity, including Rockefeller Center and Times Square.