The Democratic presidential nominee appeared to faint on her way into her van and had to be helped by her security, the source said. She was “clearly having some type of medical episode.”
Clinton's stumbled off the curb, her "knees buckled" and she lost a shoe as she was helped into a van during her "unexpected early departure," a witness told Fox News.
A separate law enforcement source told Fox News that Clinton left the event because she wasn't feeling well.
Clinton's campaign did not immediately respond to calls seeking comment.
Clinton was in New York for Sunday’s ceremony commemorating 15 years since the 9/11 terror attacks.
The Clinton campaign would not confirm Clinton’s location to an NBC pool producer. After Clinton left the ceremony, the reporters following her on the campaign trail were prevented from leaving the media area for a period of time.