Debris on the subway tracks at a midtown station delayed trains on five lines for more than two hours Thursday morning, the MTA said.

The debris and a “third rail protection board” were on the tracks north of the 50th Street station, causing service changes and delays on the 1, 2, 3, 4 and 5 trains beginning at about 7:30 a.m., the agency said.

It was unclear what caused the board to be on the tracks, but it was removed by about 9:15 a.m. Regular service was restored at 10 a.m., according to the MTA.

Commuters took to social media to share images of crowded stations, once again expressing frustration with the transit agency.

“MTA I get it - there are major infrastructure issues that you guys are working against. BUT this is ridiculous,” one user wrote.

Separately, switch problems at Queensboro Plaza and signal problems at Brooklyn Bridge-City Hall caused delays on the N, Q, R, W and 6 trains for parts of the morning commute.

“Today’s subway problems should remind [Gov. Andrew Cuomo] that even though school may have started, the summer of hell isn’t over for subway commuters,” John Raskin, executive director of the Riders Alliance, said in a statement. “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.”

Thursday’s delays were just the latest nightmare commute for New Yorkers. In August, trash that was not properly secured on a refuse train caused delays on nine subway lines during the morning commute.

And in July, trash on the tracks near the 145th Street station in Harlem caused a fire that disrupted service and left nine people with injuries.

In response to declining service, the MTA released a $836 million plan based primarily around hiring thousands of new workers to fix the signal system and other infrastructure issues this summer. Cuomo, who oversees the MTA, also raised the fine for littering in the subway system in early September and created a reliability plan with ConEd in an attempt to reduce debris- and power-related delays.

Both the office of Mayor Bill de Blasio and Nicole Malliotakis, his GOP challenger in this year’s mayoral election, weighed in on Thursday’s subway meltdown.

“Enough is enough,” tweeted the account of the mayor’s office, promoting de Blasio’s millionaires tax proposal that would fund MTA infrastructure improvements.

Malliotakis tweeted that she would make such fixes a priority of her administration.

“I will make upgrading subway signals & infrastructure a priority because [the] greatest city in the world should not have [a] 3rd world transit system,” she said.