The first ominous sign came at around 1600 local time, when the air-conditioning unit spluttered to a halt.
Then my computer-screen went a murky shade of grey: a sure sign that the power-save function had kicked in.
Heading onto the streets of Williamsburg, Brooklyn, an hour or so later, it was clear that most local shops and businesses had decided to close for the day - praying no doubt that the power would return as soon as possible before freezer-loads of food thawed out overnight.
The bridges leading out of Manhattan were overrun by crowds
I headed for the Williamsburg Bridge, one of the main arteries into Manhattan from Brooklyn, with a pleasant walkway for pedestrians over the busy roadway.
What we saw on the bridge was a shocking sight - a vast exodus of people as far as the eye could see, trying to make it home from their workplaces, trudging past paralysed subway trains.
Most of the human traffic was trying to escape the chaos of Manhattan, with not a single traffic light or power socket working anywhere.
Taking a brief time-out the change her baby Trinity's nappy on the bridge, Cathy Conley, 22, said she had been at a routine hospital appointment when the lights suddenly went out.
"I've got a pretty long walk ahead of me, but I'm used to going fast, even with my stroller," she said, strangely elated by the extraordinary spectacle all around her.
She had not managed to speak to any family, but she reckoned on making it home in about an hour.
Further along the bridge, Paul Brittle, 28, an electrician, was taking a short cut by walking along the outside of the main walkway.
"I was having a massage, when I heard someone explain that the power in the north-east was out.
"I thought they meant north-east Manhattan - then I realised they meant the whole of America," he added.
Like many I spoke to, he was concerned initially that terrorism was responsible for the power-outages.
In the dark
Helping to control the mass of people and slow-moving cars on the Manhattan side of the bridge, police officer George Lurch said the trials of 11 September - the last time that such an exodus on the bridges was witnessed here - meant New Yorkers were prepared for this kind of sudden crisis:
"In one way, this is a tragedy too. People are going to lose a lot of money.
"But everyone's behaving in a real orderly way, and hopefully it's going to stay like that," he said.
Most New Yorkers remained calm
Colin Jerolmack, 24, had cycled along the bridge to watching the whole scene unfold.: "What I'm wondering about is what's going to happen when it gets dark. It's fun now, but no-one knows what's going to happen then."
One kebab store owner, Steve Venetos, was just closing his store down on the Lower East Side, when I caught up with him: "When this happens now, I always think of terrorism, and about my 18-month old daughter.
"It's bad for business but money doesn't make a difference to me right now. I just want us all to be safe," he added.
One man watching the action on the Williamsburg Bridge, Jordan Stein, was happily listening to live radio updates.
"I live here, so I don't have to get home anywhere. Last time I saw this was September 11. It was the same , but without the smoke and the ash."