A power outage hit the White House and much of the Washington area on Tuesday, snarling trains, emptying museums and cutting electricity to government buildings and the U.S. Capitol for hours.

Many of the outages were brief, but some were longer and forced evacuations. Officials said they did not suspect terrorism in the outages or the explosion that prompted them.

At the White House, backup generators kicked on when the power went out, so the interruption lasted only a few seconds. The complex quickly went back onto regular power. Electricity in the press briefing room dipped around lunchtime, briefly darkening cubicles and blackening TV screens.

White House press secretary Josh Earnest said he understands that Homeland Security has “indicated they don’t currently see a nexus to terrorism or anything like that” in the power outages.

Robyn Johnson, a spokeswoman for the District of Columbia homeland security office, said there was speculation that an explosion about 12:30 p.m. EDT at a plant south of Washington operated by the Southern Maryland Electric Cooperative had caused a power surge that cut electricity.

The power company did not immediately respond to requests for comment.

Shortly before 1 p.m. we experienced a dip in voltage in the Washington D.C. area. This was caused by an issue with a transmission line.

— Pepco (@PepcoConnect) April 7, 2015

About 8,000 customers in Washington were affected, Johnson said. About 20,000 lost power in southern Maryland, Wanda Jackson, a spokeswoman for the Prince George’s County Office of Homeland Security.

Power company Pepco Holdings Inc said the outage stemmed from a dip in voltage because of transmission line trouble. The Department of Homeland Security said there was no indication the outages had been caused by malicious activity.

Power also went out at the State Department during the daily press briefing, forcing spokeswoman Marie Harf to finish her comments in the dark. Power in the U.S. Capitol building twice shut down briefly, then came back on by way of a generator.

Some traffic lights were out, and Metro said 14 of its 91 public transit stations were affected. Power to the trains remained on and trains were moving system-wide Metro spokesman Dan Stessel said, but the affected stations were on emergency power, with dimmer lighting and nonworking elevators and escalators.

University of Maryland officials said their entire campus was affected. Wallace Loh, president of the University of Maryland, tweeted: “There is a problem with the electric feed to campus. PEPCO is working to restore the power.”

Some Smithsonian museums were affected. The National Air and Space Museum, the National Museum of the American Indian, the National Portrait Gallery, Smithsonian American Art Museum and the Anacostia Community Museum were evacuated and closed to the public, a spokeswoman said.

Metro tweeted that several train stations were on backup power.

Story compiled with information from The Associated Press and Reuters.