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(The following article by Sewell Chan and Thomas J. Lueck was posted on the New York Times website on December 2.)

NEW YORK — A subway train derailed near Herald Square early yesterday, requiring 57 people to be evacuated and forcing some delays. But that was only the beginning.

Hours later on the same track, a string of electrical fires broke out, sending heavy smoke billowing through three subway stations and slightly injuring five people.

The ensuing disruptions played havoc for hours on travelers using two of the city’s busiest sets of subway lines. Service along Avenue of the Americas was shut down as more than 100 firefighters converged around the West Fourth Street station, where the smoke was heaviest.

Like a row of dominoes, the derailment and fires on the track used by the F and V trains created delays elsewhere in the system. At one point, the entire B and V lines were suspended. And service on the A, C and E trains was delayed as other lines were rerouted onto the tracks under Eighth Avenue.

Several commuters said they were exasperated by the subway mishaps, occurring as fares are expected to rise for the second time in less than two years.

“We’re giving them more money and we’re getting less service,” Kermit Gary, 35, said after he was turned away from the station at 14th Street. He said that walking to Eighth Avenue and using the E train instead of the F would significantly lengthen his trip to Jackson Heights, Queens.

It was unclear if the morning derailment and the afternoon fires – both on the track used by the F and V trains – were related.

Officials expressed relief that the derailment occurred in the early morning, when the trains are least crowded, and that there were no trains with passengers in the tunnels where the fires broke out. “It could have been a lot worse,” said Deputy Chief Paul Cresci, a division commander for the Fire Department.

The string of events began at 4:06 a.m., when an F train derailed 500 feet south of the 34th Street station. There were no injuries. The train operator and conductor led the passengers on the eight-car train to safety by walking them on the roadbed to the station.

The derailment occurred when the rear wheels of the fourth car on the train “passed over an improperly secured section of track that was in the process of being replaced,” said Paul J. Fleuranges, a spokesman for New York City Transit. The train, flagged along by transit workers, was moving slowly through a work area when it derailed.

Trains were rerouted as transit workers tried to repair the damaged track and place the train back on the rail. But then a new problem arose.

At 12:56 p.m., the Fire Department was called about a subway fire near West Fourth Street. Within minutes, 911 callers reported smoke at the 14th Street station and the station at Broadway and Lafayette Street.

The fires led to confusion throughout the system. About 1:55 p.m., a southbound E train passed West Fourth Street without stopping and proceeded to Spring Street, as the cars began to fill with the kind of acrid smell one might associate with burning rubber or malfunctioning mechanical equipment.

The Spring Street station itself was filled with a light, silvery haze. One woman at the south end of the subway car held a corner of her jacket over her mouth, her head bent.

As smoke filled the stations, “people left the subway fairly smoothly,” said Inspector Joseph R. Riley, the top police official at the scene. Police officers closed off several lanes of Avenue of the Americas starting at 1:13 p.m. as emergency vehicles converged on the stations. The avenue was reopened shortly after the fires were declared under control, at 2:45.

By 4 p.m., before the start of the evening rush, full service had been restored on the southbound B, D, F and V trains. The northbound F and V trains were running on the express track between West Fourth and 34th Street.

Still, the disruptions left a lingering frustration with some travelers.

Jamilatu Zakari, 20, was headed to an interview for an internship when she was forced to leave the 14th Street station. “Now I’m going to have to take a taxi,” she said. “As a student, that’s difficult for me.”

Chief Cresci of the Fire Department said it was not unusual for smoke to spread rapidly, because trains pull and push air through the tunnel network. Debris on the tracks probably caught fire from sparks along the electrified third rail, he said.

“We know we had a problem with the third rail,” Chief Cresci said. “I am speculating that was our problem, and it ran down the line while the power was on. Once the power was off the smoke conditions subsided.”

At the Office of Emergency Management, officials became alarmed as more and more calls were made about smoke in subway stations up and down the avenue.

Asked if officials had feared a terrorist attack, Robert P. Wilson, a deputy commissioner of the office, said, “That’s always at the back of the mind.”

David W. Dunlap and Johanna Jainchill contributed reporting for this article.