Authorities said the southbound train struck a tunnel wall just before 10 a.m., causing two cars to derail near the 125th-street station in Harlem.
A, C and D trains are holding in stations in both directions.
In the transport Department of NY said that the train made an emergency stop, causing the accident, was damaged the way and part of the tunnel.
According to the Metropolitan Transportation Authority, service was suspended or rerouted on several subway lines running between upper Manhattan and northern Brooklyn following the accident.
"They didn't let anybody off (except 1 car) until smoke came." tweeted Benjamin Williams. A and D trains were holding in stations in Manhattan, but service changes remain fluid. "People were falling", said passenger Susan Pak, of Englewood Cliffs, New Jersey.
Gov. Andrew Cuomo, who controls the subway system, has vowed to take emergency action to improve the system after it became clear that its aging infrastructure was failing. It said there was smoke but no fire.
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But after the stinging defeats in SC and Georgia , Democrats and liberal pressure groups are searching for what went wrong. The special elections have been held in Kansas, Montana, Georgia and SC , districts that are heavily conservative.
"Riders on the A train had a terrifying experience this morning when a train derailed", John Raskin, executive director of the Riders Alliance, said in a statement.
For now, Lhota said, service on the affected train line is suspended. "It wasn't heavy smoke, but it was frightening", he said. Emergency crews shut off track power after derailments to prevent evacuees from being electrocuted.
"People didn't panic", he said. Fire officials estimate that as many as 500 of the 800 people stuck on trains after the power outage exited the train into the tunnel on their own. Dozens of subway lines were delayed for hours after a power outage in Midtown was felt throughout the city.
Commuter railroads have also had problems recently.
This is a developing story; check back for updates and get the PIX11 News app to stay informed all day.
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