"There was a boom and a bag and a flash of light", said Jim Long from Fire Department New York.
The blast prompted a brief fire at a sprawling Con Edison facility in Queens - but no injuries - and a spectacular illumination of the NY skyline that generated a flurry of online commentary.
"Whether it was aliens, a mad scientist, a kid getting super powers, or an iPhoneX exploding I am ready for the government to cover it up".
The light show was enormous and could be seen from as far as Manhattan, with residents across the city stopping to take pictures and video to post to social media.
Public transportation is running, but the 7 train is experiencing delays, Mayor Bill de Blasio said on Twitter.
Con Edison says a couple of transformers tripped offline at the substation at 20th Avenue and 32nd Street, sparking a fire.
CBS Newspath senior producer Heather Scott reported from Astoria that the sky turned "super bright blue" and it "looked like daylight outside".
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Blue lights over the Queens borough of NY, reportedly caused by a fire at an electrical substation, December 27, 2018. "Con Edison has restored all major transmission lines associated with this event and is in the process of investigating the root cause of the failure". The utility's outage map showed only about 50 power outages as of 9:50 p.m. Thursday, but that number was growing.
Blue lights were seen around the city and in New Jersey, according to WPIX.
Karol Markowicz said: 'Wtf if this insane bright blue light over Brooklyn?!?'
The unusual sight was caused by an explosion at the Astoria power plant in Queens.
The explosion caused power outages and also impacted subway service in the area.
In the earliest moments, hundreds of Twitter users from across the city posted videos of the eerie lights, causing many on social media to fear an alien invasion.