Metro Blue and Orange Line service resumed before 2 p.m. Tuesday after being suspended when a piece fell off a Metro train and onto the tracks.
Service was suspended in a wider swath, between Federal Triangle and Federal Center SW.
A friction ring, which is part of the braking system, fell off a westbound Blue Line train between the L'Enfant Plaza and Smithsonian stations and struck the third rail, Metro spokesman Dan Stessel said. That led to sparks and smoke, but not fire, he said.
The piece also damaged two following Orange Line trains, News4's Pat Collins reported.
No injuries were reported.
Despite early rumors on Twitter, the piece was not a wheel, Stessel said.
The friction ring is a redundant system, Stessel said, meaning the train can operate without one. It fell off a 5000-series rail car. Metro will test all 194 5000-series cars to make sure none has brake problems.
Passengers were off-loaded into the Smithsonian station, but scores were stranded up to two hours, and riders told Collins they waited at least a half hour before receiving any communication from Metro.
Once inspection was completed, the train was to be removed from the tracks, Stessel said.
Since the third rails in both directions were deactivated, a couple of other trains in the vicinity were powered off as a result.
In a phone interview with News4 shortly after 11 a.m., Rhonda Bailey said she'd been stuck on a train since 9:30 a.m. She was sitting next to another passenger named Tai, who said she saw flames coming from the track.
"The next thing I knew, something went boom! and then fire.... I almost jumped in another lady's lap on the other side [of the train]," Tai said.
The train ran over something, she said, and some passengers in front of her were saying that something had fallen off the Blue Line train ahead of them.
"There was no communication from Metro," she said. "Zero. Not the conductor, not officials, nothing."
Baily also cited a lack of communication from Metro as leading to increased fear among passengers.
"Nobody communicated anything," Bailey said. "...[I]t was scary, there was smoke.... There were a few passengers who actually pried the door open.... None of the emergency buttons were working at the ends of any of the cars. Someone was able to open the doors between cars."
Andrew Strutt was also on one of those trains and tweeted about the evacuation (@r0d3ent). "They're doing a head count on us. DCPD DCFD #wmata are preparing to put us in groups and evac us," he tweeted. And later, "#wmata is accessing panels to open doors. Some doors are jammed and wont open, intercoms non-functional."
He tweeted that they were finally being evacuated about 11:30 a.m.
While firetrucks were still at the Smithsonian station, firetrucks had left L'Enfant Plaza as of 11:30 a.m., "and the lunch trucks are starting to move in," News4's Megan McGrath reported. Police vehicles are still there.
Shortly before 11 a.m., police and firefighters were still clearing out the station and firefighters were seen carrying down a piece of equipment that may have been a fan.
Metro authorities established shuttle bus service. Many people opted to walk to work if they were near enough, McGrath said.
Several intersections were briefly shut down, but have reopened.
Stay with NBC4, NBCWashington.com and @NBCWashington as this story develops.