Train service along the Northeast Corridor remained disrupted early Friday, with more than half dozen trains canceled and delays expected, after a power failure shut down all lines for more than three hours on Thursday and caused significant holdups in and out of the nation’s busiest transit hub.

Amtrak said that on Thursday, one of the hottest days of the year, the loss of electricity had forced it to suspend all service along that 150-mile stretch of rails, which passes through Pennsylvania Station in Manhattan, at about 2:10 p.m. After repairs, service was partly restored around 5:30 p.m.

The disruption rippled along the Eastern Seaboard, causing trains to be halted and canceled as far away as Boston and Harrisburg, Pa. The aftereffects appeared to continue into Friday morning’s commute, with two Acela trains and four Northeast Regional trains scheduled for as early as 4:50 a.m. canceled because of the earlier disruptions, according to Amtrak. As of 5.a.m., one other regional train in Connecticut was also canceled because of equipment issues, Amtrak said, with buses provided as a replacement.

Service on Friday was otherwise restored between Philadelphia and New Haven, but Amtrak warned that passengers could experience “significant residual delays.” Rail service in and out of New York’s Penn Station was operating “on or close to schedule,” New Jersey Transit said after Thursday’s disruptions.

Gery Williams, an executive vice president of Amtrak, said the problem emanated from “a malfunctioning circuit-breaker” in New Jersey, just west of the rail tunnels under the Hudson River, which cut electricity to the overhead wires that power trains into and out of the tunnels. That segment of the corridor has just two tracks and is the primary bottleneck for train travel in the Northeast. Any disruptions to that narrow passage can mean headaches for thousands of travelers.

Mr. Williams said the electrical problem was not related to a brush fire in Secaucus, N.J., on Thursday afternoon that was burning near train tracks and the New Jersey Turnpike. That fire was extinguished by Thursday evening.

One of Amtrak’s Acela trains was already running more than an hour late when it got stuck just east of Newark with no air conditioning, Mr. Williams added. Those passengers were transferred to other trains, he said. Another Amtrak train was stranded in Queens, also without air conditioning. Amtrak sent a diesel engine to haul that train back to Pennsylvania Station in Manhattan, he said.

Mr. Williams apologized to the customers of Amtrak and New Jersey Transit, whose trains share the portion of Amtrak’s Northeast Corridor between New York City and Trenton, N.J.

He said that he met on Thursday with New Jersey Transit officials to work out plans for upgrading the rail infrastructure “so that our customers don’t have to put up with this awful experience” again. He said there had been “too many” significant disruptions recently.

New Jersey Transit diverted trains bound for Penn Station to Hoboken Terminal and accepted train tickets on its buses during the hours it was out of service. The PATH train between Manhattan and New Jersey also cross-honored rail tickets.

Jim Casey, 59, had been waiting in the station for nearly three hours on Thursday night. The delays, he said, had thrown a wrench into his evening plan to go to the beach.

“Right now there’s one tunnel in and one tunnel out,” said Mr. Casey, who commutes to Manhattan from Bucks County, Pa. “If something goes wrong in the tunnels we’re stuck.”

Asked if he thought the situation would improve in the future, Mr. Casey did not hesitate. He was not optimistic “this problem will ever go away,” he said.

He said he was late to work Tuesday because of delays and then waited two hours after work the same day to get home

Across the river, at Newark Penn Station, Ilana Nathan was trying to travel from Long Island to her home in Cherry Hill, N.J. Her train at Penn Station in Manhattan was canceled, but then she was able to board its replacement. Then that too was canceled, but only after she’d sat on it for 90 minutes (with no air conditioning.)

A station official advised her to take a PATH train to Newark, she paid surge pricing for an Uber to the World Trade Center station. When she arrived in Newark she found all trains canceled. By then, she had been in transit for six hours.

“I’m hot, I’m exasperated,” said Ms. Nathan, 29. “I just want to go home.”

The disruption was at least the fourth in the last two months to cause long delays for commuters in the metropolitan area.

On Tuesday morning, New Jersey Transit service into and out of New York’s Penn Station was suspended for about an hour and all Amtrak trains passing through the station were delayed because of overhead wire issues and a disabled commuter train on the tracks, train officials said.

That disruption ruined the morning commute for thousands of New Jersey residents as the delays rippled out along the various rail lines in the state.

The problems on Tuesday came on the heels of major rush-hour delays at Penn Station earlier this month, caused by an inspection of tracks owned by Amtrak. Service was significantly delayed for more than an hour.

Service was also disrupted in May when an overhead wire used for traffic signals fell and struck a cable in Kearny, N.J., that provides electrical power to trains on Amtrak’s Northeast Corridor. Trains were halted on Amtrak and New Jersey Transit in both directions between Penn Station and Newark, and delays stretched to more than four hours.