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 on the West Side of Manhattan without power until late into the night. But they provided scant 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’s president, Timothy Cawley, said Sunday that, because the system was nowhere near its capacity, he was certain that the root cause was not overwhelming demand for electricity. But he said it could take weeks to fully understand why the failure cascaded from a substation on West 49th Street through neighborhood after neighborhood.

Cawley said there were redundancies built into the power grid to prevent failures from spreading, 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 service on several subway lines and shut down many of the city’s most popular sources of entertainment, including Carnegie Hall and 26 Broadway theaters, and even cut off 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 power loss.

Sen. Chuck Schumer, a Democrat, called for the U.S. Department of Energy to investigate the utility 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 Sunday morning from Iowa, where he had been campaigning for the Democratic nomination for president.

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

The mayor expressed support for Schumer’s call for a federal inquiry.

“We’re going to hold Con Ed’s feet to the fire,” de Blasio said. “We’re going to work very close with them. But, look, if the Department of Energy has something to offer, of course we want as many eyes on the situation as possible.”

No one was 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. 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 department 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.

The police commissioner, James P. O’Neill, said he sent more than 400 additional officers to the area affected by the blackout, including 16 who worked on a task force assigned to elevator rescues. He also dispatched 100 extra traffic agents. The response required pulling one squad car from each of the city’s 77 precincts — a difficult task on a Saturday night, O’Neill said.

Andy Byford, the chief executive of the New York City Transit Authority, said he was in Brooklyn when he heard that the lights were going out in Midtown Manhattan. He and Veronique Hakim, the authority’s managing director, went to the subway control center and oversaw the rescue of 2,875 passengers from three D trains and two A trains, Byford said.

With power still flowing to the third rails but not to the system’s signals, the trains had to be guided forward to the next station, where riders stepped off onto platforms. Byford said none of them required medical assistance. He said five people were rescued unharmed from an elevator at the 34th Street-Hudson Yards station.

“This was the biggest incident that we faced on my watch,” Byford said.

At Con Edison’s control room in Midtown, Cawley said, trouble was first detected Saturday evening when circuit breakers popped opened and “de-energized” the West 49th Street substation. The disruption quickly affected five networks that distribute electricity within particular neighborhoods, including Midtown West, Rockefeller Center and Times Square. Power was lost in an area that stretched south from 72nd Street between the Hudson River and Fifth Avenue. Eventually, a sixth network, serving the area around Pennsylvania Station, also failed.

Cawley said some of the utility’s equipment might have been damaged, but “the grid is sound.” He said the last time there had been a similar failure that did not have an external cause was 13 years ago.

The mayor praised Con Edison for its speedy restoration of service, but Gov. Andrew M. Cuomo, a Democrat, was more critical. Cuomo said in a radio interview Sunday on WINS-AM (1010) that he would have state investigators conduct an independent review of the failure, which he called unacceptable.

“You lose power, chaos is right around the corner,” Cuomo said.

The blackout shut down 26 Broadway shows, but all of them had returned to their regular schedules by the Sunday matinee, according to the Broadway League, a trade association.

“It costs a fortune to run a small business in New York City, and when you lose a big Saturday night, it definitely hurts a small business’s bottom line,” said Andrew Rigie, executive director of the New York City Hospitality Alliance, a trade group.

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, Berkley said. 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,” he added.

Despite the hardships of a Saturday evening in July without electricity, Corey Johnson, a Democrat and the speaker of the City Council, gave New Yorkers high marks. “We had a really textbook response where things went well,” he said.

This article originally appeared in The New York Times.