More than 70,000 people were affected by a massive power outage in parts of New York City on Saturday evening which saw the screens at Times Square go black and left cinema-goers sitting in pitch-black movie theatres, according to U.S. media reports.

Midtown Manhattan and the Upper West Side were affected.

“We are responding to extensive outages on the Westside of Manhattan,” a spokesman for energy supplier Con Edison tweeted.

Shortly before midnight, New York Mayor Bill de Blasio said power had been restored.

“Power was restored to remaining customers,” the mayor tweeted around midnight. “I want to thank all of our first responders, the men and women of the NYPD, FDNY and @NYCEmergencyMgt for their hard work tonight — and every New Yorker for responding to the black out with that trademark NYC grit and toughness.

During the Saturday evening blackout, elevators were stuck and traffic lights were out while some subway stations were closed, local media reported.

Several Broadway shows were cancelled at short notice.

Some artists gave impromptu performances on the pavement outside theatres.

A concert at Carnegie Hall resumed in front of the building once the audience had reassembled outside.

While many stores closed early, lots of bars and restaurants stayed open. Some of the electronic billboards on Times Square went dark.

There were no reports of people injured and no reported arrests.

De Blasio earlier said the power outage appeared to be the result of a mechanical problem in the electrical grid.

“This appears to be something that just went wrong in the way that they transmit power from one part of the city to another,” the mayor told CNN. “It sounds like it is addressable in a reasonable amount of time.”

The mayor was campaigning in Iowa and was due to return to New York late Saturday, his campaign press secretary told the U.S. broadcaster.

Firefighters were responding to numerous transformer fires as well as people trapped in elevators and subway cars, a Fire Department spokesman told CNN.

The power failure occurred 42 years to the day of an extensive blackout that affected much of New York City in July 1977, sparking arson attacks and looting.