Power was restored to most of New York City late Saturday night, after a major blackout struck in parts of midtown Manhattan and the Upper West Side left some 90,000 customers without power.

"An estimated 10K customers remain without power as restorations progress. Remaining customers are expected to see power back in the next hour,” said New York Mayor Bill de Blasio.

The city's transit authority tweeted that multiple stations were not operational and were being bypassed, NBC News reported.

The outage occurred on the anniversary of the citywide blackout of 1977, which led to rioting and looting. That outage started on July 13 and ended the next day.

"We are working with Con Edison to determine the root cause of the ongoing power failure, which is affecting Midtown and the Upper West Side," the New York City Transit Authority tweeted.

A senior city official with direct knowledge of the matter said it appears the outage was caused by a transformer fire. New York's fire department, FDNY, tweeted it was at the scene of a transformer fire on West 64th Street.

De Blasio, who is in Iowa campaigning for the Democratic nomination for president, confirmed the cause and said no foul play was suspected.