NEW YORK – New York City and Con Edison officials are befuddled over what caused Saturday night’s blackout on Manhattan’s west side, which left hundreds of thousands without electricity and subway service.

Mayor de Bill Blasio told reporters Sunday the outage was not caused by a cyber attack or an act of terrorism, and Con Ed officials will have to go through reams of data to determine a root cause. High electricity demand and the old age of the city’s electrical grid were also not to blame, officials said.

Con Ed president Tim Cawley said a major electrical transmission substation on West 49th Street stopped producing power — he did not know why.

“(We need to determine) why did that ring bus, the major transmission distributor, fail last night,” said Cawley. “We designed the system such that for the loss of any two major components we could still run the system on the hottest day of the year. There’s incredible redundancy in terms of capacity.”

Cawley said crews will have to go through bundles of data, organize it and begin building a timeline of what happened leading up to the blackout. He called it “painstaking” work, and noted it would not be finished for weeks.

“We’ll understand the dynamic of the grid, and why a failure of one component led to a much wider impact on the system,” said Cawley.

De Blasio said he will be working closely with Con Ed officials this week as electricity demand is expected to peak while temperatures rise into the 90s.

The mayor said he’ll work with Con Ed to complete its analysis of the blackout’s cause, and that he will provide the public with any major updates as new information surfaces.

“When that analysis is complete, and we’ll do it in stages, any changes that are needed in terms of changing the physical approach, new regulations, whatever it may be, we’re going to get to work on immediately,” said de Blasio. “But it will take some time to make sure we get exactly right what happened here.”

Gov. Andrew Cuomo said he does not trust Con Ed’s analysis and is sending in independent investigators for a second look.

“I’m not interested in Con Ed’s explanation,” Cuomo said on NY1 Sunday. “I don’t believe Con Ed was adequately prepared.”

Cuomo said that other substation explosions like the one that blew up in Astoria, Queens, in December demonstrated Con Ed’s record of incompetence.

Sen. Chuck Schumer on Sunday called on the U.S. Department of Energy to investigate the outage, but de Blasio said he does not trust the Trump administration to honestly assess the situation.