The Hunger Games star had been appearing on The Late Show With David Letterman in the US and stopped to greet fans afterwards.
But according to Us Weekly, when she was led away from the crowds and then ran back to sign more autographs, there was so much excitement that the barrier holding her fans back toppled over.
Minders had to whisk J-Law away from the scene before the crowd got out of control.
Earlier on the show, the actress had revealed her lack of singing talent when talking about having to perform a song in The Hunger Games: Mockingjay Part 1.
She said: "I do not like singing in front of other people, that's like my biggest fear. I cried on set that day. I'm scarred from my childhood. I have a Southern mother that used to tell me I was amazing at everything and I could do everything, but I can't. I had this tone-deaf-Amy-Winehouse voice and I sang in front of the school when I was eight, because I thought I could."
Jennifer said the song she had sung was Have A Holly Jolly Christmas, and gave a rendition of part of it in a growling voice, saying: " My dad laughed for the entire week. I'd hear him around the house, imitating me. I hate it, I hate it!"
Jen added of her Hunger Games song: "It was called The Hanging Tree, which was where I wanted to go."
She said she had wanted Lorde, who sings on the soundtrack, to be dubbed over her scene: "I was like, will you guys please get Lorde and lip-sync it? And they said no, so it's really me, but I've avoided that scene."
