Service on the A train between the Jay Street/MetroTech and 207th Street stations was suspended while the C was not running at any point along the line.
Investigators are trying to figure out why an emergency brake suddenly activated and derailed a southbound A train near West 125th Street and injured more than 30 people Tuesday morning, officials said.
Passengers on one train tell WABC that it felt like it jumped off the tracks at around 125th Street.
This story was updated at 2pm to include updated injury reports, additional trains halted, and images.
The accident quickly rippled throughout the system, causing long delays on a number of lines, with some commuters reporting being stranded on subway cars underground for more than an hour.
A sudden braking caused a train derailment in Harlem, injuring 30 people and causing massive transit disruption.
"It's a serious derailment, with quite a bit of damage to signals and some structural damage to the walls", he said.
Almost three dozen people suffered minor injuries in the derailment, which happened in Harlem just before 10 a.m.
At the time of the derailment, passengers reported their train vehicle filling with smoke, and some panicked straphangers forced their way out of the cars onto the tracks, reported the NY Daily News.
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The fire and police departments conducted a joint operation - involving 300 responders - in order to round up the passengers and bring them above ground, Nigro said.
Passengers were evacuated from the derailed train, as well as three other trains, including one C and one D, that were also in the tunnel at the time, the MTA said.
"People didn't panic", he said.
The MTA added that three disabled trains had been evacuated and passengers were taken safely above ground.
"The emergency brakes automatically went on".
It's clear we have an outdated and crumbling public transit system.
He said the station was not smoky, but there was a strong, acrid smell.
Subway service was disrupted for hours and there were several minor injuries.