A Manhattan power outage that temporarily turned off the bright lights of the big city lasted only a few hours but left plenty of lingering questions and calls for investigations Sunday.

Con Edison President Timothy P. Cawley insisted the Saturday night blackout that darkened more than 40 blocks of Manhattan, including Times Square, wasn’t caused by high demand on the electrical grid but said it would take time to determine what exactly did happen.

“We think the grid is sound,” Cawley said Sunday, adding that “if there are lessons we can apply, we will.”

He said the system was prepared to deal with high demand like that expected this coming week as temperatures rise.

Officials definitively ruled out either cyber or physical acts of terrorism.

Thousands of people crowded the streets Saturday evening, using their cellphones as flashlights while they tried to stay cool amid the humid July evening, when temperatures hit the low 80s. According to Bloomberg News, the outage struck at 6:47 p.m., lasted until about midnight and affected almost 73,000 customers.

In the theater district, marquees darkened just before evening performances were set to begin. Most Broadway musicals and plays canceled their Saturday evening shows, though some cast members staged impromptu performances in the street.

U.S. Sen. Charles E. Schumer (D-N.Y.) said Sunday that the Energy Department’s Office of Electricity should investigate the work being done by Con Ed to maintain and upgrade the city’s power grid.

He added that “this type of massive blackout is entirely preventable with the right investments in our grid,” encouraging a thorough investigation that could shed light on wider electricity issues that could have national impact.

Gregory Reed, a professor of electric power engineering at the University of Pittsburgh who once worked at Con Ed, said the utility had done a good job in restoring power quickly but said it underscores a need throughout the country to invest more in infrastructure. “We have a lot of networks that have aging infrastructure and antiquated systems,” he said. “We have to build higher levels of resiliency.”

New York Gov. Andrew M. Cuomo (D) and New York Mayor Bill de Blasio (D) both said they would be directing agencies under their control to look into what happened.

Cuomo, expressing frustration over what he described as repeated failures of Con Ed’s system, said in an interview with ABC News that he was sending his “top power team” to investigate the incident, according to Bloomberg News.

“If they don’t give me an answer quickly, I’m going to go to Con Ed headquarters,” he said. “If I don’t get a firm answer forthwith, I’ll go speak to Mr. Con Ed myself.”

The questions raised by the blackout weren’t just about the power; they were political, as well. De Blasio was criticized for being on the presidential campaign trail when the outage happened.

He returned to the city Sunday and insisted that the situation had been well managed, that he had been in touch with his staff and that he started his trip back as soon as it became clear the blackout would not be quickly resolved. “You have to take charge wherever you are, and I did that,” he said.

The outage stymied subway service throughout the city, affecting nearly every line. New York City’s Emergency Management Department said many trains had resumed running in both directions by about 2 a.m. Sunday.

No injuries were reported.

The police and fire departments brought people and equipment in from other parts of the city to help, including 400 police officers and 100 traffic agents, as well as 93 additional ambulances.

The outage came on the anniversary of the 1977 New York outage that left most of the city without power.

Just over six months ago, Con Ed was facing an investigation after an electrical fire at a substation turned New York’s night sky blue, temporarily disrupting flights and subway services, Bloomberg News reported. In July 2018, it was the subject of a probe after an asbestos-lined steam pipe ruptured in Manhattan’s Flatiron District. And a power failure in 2017 led to significant delays on the subway during a morning commute, triggering a probe that cost the company hundreds of millions of dollars.

— Associated Press