NEW YORK >> Swarms of furious commuters packed subway platforms from the Bronx to Brooklyn today after at least eight lines on New York City’s dilapidated subway system were snarled by problems that included debris on the track and signal woes.

The delays underscored the challenges confronting the century-old system even as emergency measures have been taken to improve the subway following a summer of meltdowns and derailments.

The problems on Thursday, which appeared to be the most serious in recent weeks, came after Joseph L. Lhota, the chairman of the Metropolitan Transportation Authority, introduced a revelatory concept to the subways a few months ago: a promise of clear, factual, over-the-loud-speaker explanations of what exactly was going wrong. The move was in response to a flurry of complaints that the agony of delays was compounded by riders being left in the dark.

The debris on the track was on the Seventh Avenue line — used by the 1, 2 and 3 trains — in Manhattan just north of the 50th Street station early this morning. The power was turned off when a southbound No. 3 train was forced to activate its emergency brakes after running over the debris, according to Marisa Baldeo, a spokeswoman for the Transportation Authority. Passengers on the disabled 3 train were stuck underground for nearly an hour until power was restored and the train was able to reach the Times Square station.

Another train that was directly behind the train that hit the debris rolled backward to the 72nd Street station, where its passengers disembarked.

The transit agency was investigating what the debris was. But a spokesman, Kevin Ortiz, said a protective cover for the third rail played a role in triggering the problem. The issue affected service on the Nos. 1, 2, 3, 4 and 5 lines. In a separate incident in Queens, a switch problem at Queensboro Plaza upended service on the N, R, Q and W lines.

The subway woes did not go unnoticed in City Hall, where the office of Mayor Bill de Blasio, who has been feuding with Gov. Andrew Cuomo, who controls the subway, posted a tweet acknowledging riders’ pain: “New Yorkers are facing delays on at least 8 subway lines this morning. Enough is enough.” The post featured photographs of riders cheek-to-jowl on platforms.

The mayor and the governor, who have had a frosty relationship on a variety of issues, have engaged in a war of words over how to finance improvements for the beleaguered subway and who should assume responsibility.

John Raskin, the executive director of the Riders Alliance, an advocacy group, said in a statement today: “Governor Cuomo produced a short-term plan to address delays, but he now needs to step up with a long-term plan to modernize the transit system and a reliable funding source to make it possible. If the governor doesn’t follow through on his promises to modernize the transit system, the ‘Summer of Hell’ could easily become a ‘Decade of Despair’ for millions of New Yorkers.”

For some riders, delays have become almost an expected part of their commuting experience.

“It’s kind of passive acceptance at this point,” said Nicholas Sawicki, 23, who waited on the 168th Street platform Thursday morning amid a group of unhappy commuters for 40 minutes. “You still have to get to work and everybody understands that the subway has just been collapsing in on itself.”

It usually takes Sawicki, an assistant at a magazine, 22 minutes to commute from Washington Heights in Upper Manhattan to his office in Midtown. Today it took about an hour and a half, he said, with half of that time spent inside the jammed 168th Street station making his way to the elevators to transfer from the 1 train to the C train. Announcements by transit workers were more clear than usual, he said, and they helped him figure out the next steps on his snarled commute. But they did little to appease frustrated riders.

“The overhaul of the entire system is such a monumental task, and talk is especially cheap in election years,” Sawicki said. “It’s an issue that has been ignored for 60 plus years,” he added. “We are the inheritants of that ignorance.”

As crowds of riders piled up across the system, many took advantage of the newly Wi-Fi enabled tunnels to vent.

At the 72nd Street station at Broadway in Manhattan, a train conductor advised stranded riders to take a bus or the B or C trains near Central Park. Some commuters preferred to give up on public transit entirely and walked instead.

As the morning wore on, social media was rife with the familiar comments, photos, videos and the hashtag #fixthesubway.