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An explosion at a power station Tuesday left the White House, the Capitol and the State Department briefly without electricity Tuesday as part of a widespread outage in Washington and its suburbs.

Patrons were evacuated from the Smithsonian, the National Portrait Gallery, the Air and Space Museum and the National Museum of Natural History, and the Metro transit system said that 13 of its stations were operating on emergency lighting.

Power utility Southern Maryland Electric Cooperative said the outage originated just before 1 p.m. ET at its Charles County, Maryland, switching station, where a 230-kilovolt transmission conductor broke free from its support structure. The failure interrupted service to other stations.

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The Department of Homeland Security said there was no immediate reason to believe the blackout was terror-related or a criminal act.

At least 9,400 customers in Washington and suburban Maryland were in the dark, according to two power companies Pepco and Southern Maryland Electric Cooperative. But federal officials put the number at as many as 28,000 customers.

Pepco, in a statement, called it a “momentary outage” and said that some customers switched to backup power systems.

At the White House, the lights dimmed in the press briefing room before backup power kicked in. Josh Earnest, the White House press secretary, said that President Barack Obama was unaffected.

The State Department's daily briefing was cut short because of the blackout, while the U.S. Capitol complex was running on a backup generator, a congressional aide told CNBC. Power was back on at the State Department before 2:30 p.m., tweeted spokeswoman Marie Harf.

The University of Maryland in College Park also reported that lights were out on campus. The campus closed for the day.

In addition, power was lost while Oprah Winfrey was giving a speech in D.C. to commemorate the U.S. Postal Service unveiling a new Dr. Maya Angelou "forever" stamp. While the room remained dark and the microphone lost audio, Winfrey kept going — to the delight of the audience.

SOCIAL

There is a campus-wide power outage. Crews are working on addressing the problem. Thank you for your patience. — Wallace D. Loh (@presidentloh) April 7, 2015

A major power outage in DC is affecting some of our museums. @NPG, @americanart @airandspace and @SmithsonianNMAI are now evacuated — Smithsonian (@smithsonian) April 7, 2015

.@marieharf having to shine phone light on reporters asking questions here. pic.twitter.com/TF4lJYSsZX — Alex Mallin (@alex_mallin) April 7, 2015

Oops! power just went out as Oprah was wrapping up her remarks at the Maya Forever stamp ceremony — Jennifer Vasquez (@JennVasquez_DC) April 7, 2015

@nbcwashington people being evacuated out of their buildings downtown due to a power outage 20th st nw and e st nw pic.twitter.com/HrOlrzvLkb — NBC PHOTOG (@bforte22) April 7, 2015

— NBC News