Officials of Con Edison, which operates the city’s power grid, said there was “a significant electrical transmission disturbance” at 6:47 p.m. Saturday that left 72,000 of its customers in Midtown Manhattan without power until late into the night. But they provided no more insight into the underlying cause of the failure, which came on the 42nd anniversary of one of the most infamous blackouts in the city’s history.

Con Edison officials said Sunday the agency would conduct an investigation “to determine the root cause of the incident.”

Tim Cawley, president of Con Edison, said there are redundancies built into the power grid to prevent failures from cascading, but “this event sort of got past that, and resulted in a large outage at the west-side station.”

The sudden loss of power disrupted five subway lines and shut down many of the city’s most popular sources of entertainment, including Carnegie Hall and many Broadway theaters, and even cut off the performer Jennifer Lopez, midsong, during a sold-out concert at Madison Square Garden. New Yorkers and tourists flooded into the darkened streets while elected officials rushed to castigate Con Edison for failing to contain the failure before it spread.

Sen. Chuck Schumer, a Democrat, called for the federal Department of Energy to investigate Con Edison and how it has invested in the city’s power grid. “This type of massive blackout is entirely preventable with the right investments in our grid,” Schumer said Sunday.

Mayor Bill de Blasio returned home from Iowa, where he had been campaigning for the Democratic nomination for president.

“There are no remaining disruptions to either traffic or transit,” de Blasio said at a news conference Sunday afternoon at a Con Edison control center in Manhattan. “Things are back to normal.”

He reiterated that there was no indication that terrorism played a part in the power failure, and he added that the system was not overloaded by energy demands. “This was not a cyberattack, and this was not an act of physical terrorism,” de Blasio said.

No one was hurt or injured as a result of the power failure, but it was a bad time to be on an elevator, according to the Fire Department.

Firefighters and paramedics responded to about 900 emergency calls stemming from the blackout, ranging from structural fires to automatic alarms, according to agency data from 7:30 to 11:59 p.m. About 400 of the calls involved people stuck on elevators, the fire commissioner, Daniel A. Nigro, said.

“Some of them were quite difficult involving breaching and blind shafts,” he said, adding that everyone was removed safely.

About 700 of the calls came over the city’s 911 system, while the remaining 200 were verbal requests made as firefighters and paramedics were tending to other calls. Jim Long, a spokesman, said resources, like fire trucks and ambulances, were moved from other parts of New York City to assist with the “very large spike” in calls.

“There were no injuries, no fatalities, no one got crushed,” Long said, adding that “we responded to many of them and dealt with them in short order.”

Con Edison said the failure apparently stemmed from a problem at a substation on West 49th Street and affected six local networks that distribute electricity within particular neighborhoods, including Midtown West, Rockefeller Center and Times Square. Power was lost in an area that stretched from 72nd Street down to 32nd Street and from the west end of Midtown to Sixth Avenue.

John McAvoy, Con Edison’s chairman and chief executive, suggested there had been a mechanical failure, but emphasized that the utility would not know the cause until an investigation was completed.

Gov. Andrew M. Cuomo was more specific, saying the failure started with an explosion and fire at a substation that caused other substations to “lose power and malfunction.”

Richard Berkley, executive director of the Public Utility Law Project of New York, a consumer advocacy group, said the power failure raised the question of whether Con Edison had placed enough emphasis on the resilience of its system.

Con Edison is asking state regulators for electric and gas rate increases that add up to about $1.5 billion, Berkley said, and Saturday night’s failure could affect the outcome of that case.

Regulators have penalized the company for blackouts in the past. In 2007, the state Public Service Commission hit the company with an $18 million penalty for power failures, including a nine-day blackout in Western Queens in 2006.

Before Hurricane Sandy struck the city in 2012, Con Edison spent “a tremendous amount of money” on the reliability of its system. But the storm proved there were serious problems with its resiliency, showing that Con Edison needed to work on “keeping one area of failure from taking down the whole system,” Berkley said.

Cuomo faulted Con Edison on that score Saturday night, saying that the utility should be better able to contain trouble.