Jennifer Lopez was forced to cancel a gig after a huge power cut swept across New York.

The 49-year-old had only just started her show at Madison Square Garden on Saturday when the power outage hit, and fans were immediately evacuated from the venue.

Lopez later took to Instagram to share an emotional message explaining her devastation after the show was scrapped.

"The power is out in NYC and at MSG. Heartbroken to say tonight’s show is cancelled. We will reschedule. Love you all!!! Stay safe!" she captioned the clip.

"We had just started our show," the Jenny From The Block hitmaker explained in the video. "They're asking everybody to evacuate, very slowly and calmly, and obviously that's what were going to have to do."

She then posted a second message on social media further expressing her disappointment.

"Devastated and heartbroken that I can’t perform for all of you tonight. We will make this up to you, I promise! I love you!!" Lopez shared.

TV presenter Gayle King, who at the singer's gig at Madison Square Garden concert when the power cut happened, posted a video to her Instagram documenting the aftermath of the incident.

"Uhhh yeah so I actually made it to @jlo concert and then what had happened 'wuz' swipe left... now wondering (sic) the streets in an Uber trying to find a hotel room," she wrote. "My apt has NO power and I live on the 27th floor ... funny thought my place had a back up generator …"

The blackout left more than 73,000 people without power, according to NBC New York.