One person died and dozens more were taken to hospitals after smoke filled a subway tunnel and a major Metro station in Washington, D.C., on Monday afternoon and forced evacuations, officials said.
Eighty-four patients were taken to hospitals and more than 200 people were evaluated for possible injuries after the incident at one of Washington's busiest rail stations, fire officials said on Twitter. One firefighter was injured.
Washington Metropolitan Area Transit Authority officials said the National Transportation Safety Board had opened an investigation.
The incident, which started about 3 p.m., was caused by an electricity-related problem, NTSB investigator Mike Flanigon told reporters Monday night.
A southbound Yellow Line train stopped for a still-unknown reason about 800 feet beyond the platform at the L'Enfant Plaza D.C. Metro rail station, Flanigon said.
About 200 or 300 feet beyond where the train halted, "there was an electrical arcing event" involving the electric third rail that powers the trains and the supply cables leading to that rail, he said.
Asked whether investigators saw evidence of anything suspicious, Flanigon said no.
A spokesman for the Fire Department did not respond to requests for comment and rail officials did not disclose the nature of any injuries.
Social media photos showed haze filling the underground station, which is near the National Mall and the Smithsonian National Air and Space Museum. Photos also showed smoke filling the cabin of a train that Metro spokeswoman Caroline Laurin said had stopped in a nearby tunnel as a precaution.
Firefighters evacuated the station as well as the passengers stuck in the train, Laurin told the Los Angeles Times.
"That was easily the worst Metro ride of my life," tweeted one rider, who identified himself as Jonathan Rogers, posting photos of firefighters and passengers in a darkened cabin and then evacuating down a dark subway tunnel. "Worst part? I got on the Yellow Line by accident."
Portions of both the Green and Yellow lines, which share a track running through the station, were shut down so officials could investigate the source of the smoke.
The smoke cleared after officials turned on exhaust fans in the station and deactivated the electric third rail, Laurin said.
Times staff writer Lauren Raab contributed to this report.