Flights into six US and Canadian airports have been stopped. Many New Yorkers, who thought there had been another terrorist attack, could not get home for the night.
Although power is slowly returning to the area, officials are warning it could still be some time before it's back to normal.
Were you caught in the power cut?
"I was at camp, on the bus back from a water park, when there was an annoncement on the radio saying that the power was out from New York City up to Canada. I really didn't think much of it until we got back to camp and we had no power.
My mom picked me up early and I skipped cheerleading practice to drive to another town to get gas for our generator. We got $40 worth of gas and when we got back, the power was back on. So much for that!"
Danae, 14, New York
"I really think that when the electricity was cut off it gave millions of people a reality check. I know it did for me. We really learned how much we depend on electricity, and how we really should be conserving it."
Cindy, 13, Canada
"I didn't know we had a blackout until my new neighbour came over in a panic because she didn't have electricity and didn't know what was going on. When I found out, my first thought was 'Great, we have a blackout' because my town used to get blackouts all the time just because of a gust of wind, but it was fixed so we haven't had any blackouts in a couple of years.
So I stayed outside with my sister just hanging out when my mom sent my sis, my bro, and me to the store to get food that didn't need the fridge or the freezer. So we went and when we came home we played Monopoly, I lost. At about 9pm we walked around town a little bit and looked at the stars, they were so bright. It was awesome. We came home around 9:45pm and I read a little bit and went to sleep at around 10:15. It was a good day even though we had no electricity."
Sara, 14, Long Island, USA
"We thought for sure that it was terrorists. But we then realised by getting some info from friends that it wasn't. We ended up playing monopoly by my booklight."
Kristine, 11, Walton, USA
"I live in Ontario, Canada. I was watching TV when suddenly the screen went black and all the lights started to go off. We had had a black out like this at the end of June, but the power returned within a few hours. However, we only got the power back here between midnight and 2 a.m.
I was supposed to work yesterday at the library, but it was closed. All the shops downtown were closed. There is a festival going on in my town and there was supposed to be a parade so I don't know if it went on. As it got darker, my family and I started to light candles. It was really nice to look up at the stars and the moon without any city lights :o) We have been listening to the radio since yesterday to keep updated on what's happening in Canada and the U.S. I hope the power continues to return because some places are still without power. Only 50% of Ontario has power!
Avishka, 15, Ontario, Canada
"It was so insane when the power went out, I live by a major intersection and there wasn't a police officer there for about an hour after the outage. It took my family ages to find a restaurant that had power cuz we couldn't even cook. People were just driving around cuz it was better than sitting at home doing nothing. The stores all sold out of ice, batteries and flashlights. It was hell. Our power went back on at 2:00 in the morning."
Kim, 17, Endicott, NY, USA
"I was at the pool when the power went out. The lights went off, the pool pump and everything, but nobody really realized what was happening. Thirty minutes later I was going back home with my bike and I nearly got run over by a car since the traffic lights weren't working...there were normal people trying to help out with it and it was pretty cool of them!
When night came I had a great time! Everything was just so strange in the dark...but the best thing to see was the dark city! It was so beautiful! Down my block, guys were selling light sticks and kids where making the most of their fire works! I have to get offline now 'cause I'm not suppose to use electricity!"
Alizee, 13, New York, USA
"I think that everyone is acting great! Everyone was practically walking home in 30 degrees celcius weather and restaurants were giving out water and food, and people were letting people sit in their cars for a/c and people were even directing traffic, everyone also handed out food and drinks to police as they were monitoring the streets, everything was very well handled by the police, government, and the citizens of Ontario."
Jenny, 13, Toronto, Ontario Canada