New York City subway riders evacuated from 4 trains after emergency brake incident; 34 injured

— -- A morning commute for New Yorkers turned into a chaotic scene today when a subway scraped the side of a tunnel wall, prompting passengers to evacuate and walk underground through the smoke and darkness.

The southbound A train was just outside the 125th Street station in Harlem when the emergency break automatically turned on, according to Joe Lhota, chairman of the Metropolitan Transportation Authority. The train bucked forward and backward, causing two of the train's eight cars to derail and scrape the side of the wall, Lhota said. The train was 200 feet from the 125th Street and St. Nicholas Avenue station at the time.

That train was evacuated, Lhota said, as were three other trains in the same tunnel.

A total of 34 people were injured. Officials said most of the injuries involved smoke inhalation and none were life-threatening. Lhota said the smoke was caused by sparks and the garbage and sanitation along the tracks.

The incident, described by the New York City Emergency Management Department as a partial derailment, caused a power outage affecting all six tracks from West 119th Street to West 125th Street.

Fire officials estimated that up to 500 of the 800 people who were on the trains left voluntarily. The FDNY was able to assist those riders before the trains returned to their stations.

Fire Commissioner Dan Nigro called walking on the tracks a "dangerous thing” to do.

Lhota said investigators will determine why the emergency brake turned on.