Hillary Clinton had a “medical episode” that required her to leave a 9/11 commemoration ceremony early on Sunday, a law enforcement source who witnessed the event told Fox News.

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.”

After more than an hour of radio silence, Clinton's campaign issued a statement saying the former Secretary of State "felt overheated."

"Secretary Clinton attended the September 11th Commemoration Ceremony for just an hour and thirty minutes this morning to pay her respects and greet some of the families of the fallen," Clinton spokesman Nick Merrill said. "During the ceremony, she felt overheated so departed to go to her daughter's apartment, and is feeling much better."

But a witness told Fox News that Clinton stumbled off the curb, her "knees buckled" and she lost a shoe as she was helped into a van during her "unexpected early departure."

MORE ON #HILLARY per witness: "unexpected early departure"; she stumbled off curb, "knees buckled", lost a shoe as she was helped into van

— RickLeventhalFoxNews (@RickLeventhal) September 11, 2016

The NYPD was sent to retrieve Clinton's shoe, NBC reported.

A separate law enforcement source also told Fox News that Clinton left the event because she wasn't feeling well.

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.

Clinton was in New York for Sunday’s ceremony commemorating 15 years since the 9/11 terror attacks.

Clinton and Republican presidential nominee Donald Trump earlier greeted supporters as they entered the downtown Manhattan 9/11 memorial. Both had promised to suspend campaign activities to mark the 15th anniversary of the attacks.

Fox News’ Rick Leventhal and The Associated Press contributed to this report.