Con Edison has yet to figure out why a large swath of Manhattan’s West Side was plunged into darkness by the blackout that lasted more than five hours on Saturday night.

In a statement released late Sunday morning, the power company said it “will be conducting a diligent and vigorous investigation to determine the root cause of the incident.”

“Over the next several days and weeks, our engineers and planners will carefully examine the data and equipment performance relating to this event, and will share our findings with regulators and the public,” the company said.

Con Ed spokesman Alfonso Quiroz blamed the blackout on a “disruption on the transmission side” of the company’s power grid.

Con Ed’s overhead transmission lines carry 438,000 volts of electricity to substations where the power is lowered to about 13,000 volts before being distributed to homes and businesses, he said.

Officials initially suspected a manhole fire that affected an underground transformer, but Quiroz said there’s “no evidence of a fire at this point.”

The blackout stranded people on subway trains and elevators, and forced the evacuation of Madison Square Garden and cancellation of Broadway shows.

It struck on the 42nd anniversary of a massive power outage in 1977 that affected the entire city and sparked looting, robberies and other mayhem.

Saturday night’s incident also occurred while Mayor Bill de Blasio was campaigning in Waterloo, Iowa, as part of his long-shot presidential bid.

Con Ed has said a series of outages that began before 7 p.m. Saturday cut power to 73,000 customers served by six electrical networks on Manhattan’s West Side.

The affected area stretched from West 30th Street to West 72nd street, and from the Hudson River to Fifth Avenue.