Democratic presidential candidate Hillary Clinton reportedly suffered a “medical episode” at a memorial ceremony held in New York on Sunday to mark the 15th anniversary of the deadly September 11 terror attacks. She left the memorial ceremony “unexpectedly” after feeling “overheated,” her campaign later said.

She was standing in a crowded area with several other politicians, including New York Mayor Bill de Blasio and her Republican opponent Donald Trump, when, at about 9:30 a.m., her aides led her away from the ceremony at the World Trade Center into a parked van.

Details of the incident were not immediately clear because there was only a small pool of reporters at the event and they did not witness the incident, Politico reported.

But quoting an unnamed law enforcement source, Fox News later reported that Clinton suffered a “medical episode” and had to leave abruptly.

According to Fox News reporter Rick Leventhal, a witness, who claimed to have been standing about 15 feet away as Clinton was being led into a van, said she stumbled on a curb, her knees buckled and she appeared to faint. She reportedly lost a shoe as she climbed into the van. An aide recovered the shoe from beneath the van which left the venue about an hour after she arrived.

Democratic presidential candidate Hillary Clinton was attending a 9/11 memorial when she alleged suffered a "medical episode.' [Image via Marianne Campolongo/Shutterstock]

She was taken to the apartment of her daughter Chelsea, according to Clinton campaign spokesperson Nick Merrill.

A video uploaded to Twitter, reportedly taken as Clinton was leaving the site of the 9/11 ceremony (see above), appears to show her unsteady and stumbling as she entered the van. Her handlers can be seen in the video supporting her as she climbed into the van.

Hillary Clinton 9/11 NYC pic.twitter.com/q9YnsjTxss — Zdenek Gazda (@zgazda66) September 11, 2016

Breaking News: Report: Hillary Clinton Leaves 9/11 Memorial Service Early Due To ‘Medical Episode’https://t.co/Y2MgakpG4Z — Fox News (@FoxNews) September 11, 2016

Her aides did not immediately explain why she left the service until about 11 a.m. when Merrill said she “overheated” and had to be taken to the New York apartment of her daughter, Chelsea.

Merrill added that the former Secretary of State was feeling better.

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

BREAKING: law enf source: Hillary Clinton just left 9/11 ceremony w/medical episode, appeared to faint on way into van, helped by security — RickLeventhalFoxNews (@RickLeventhal) September 11, 2016

“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,” Merrill said. “During the ceremony, she felt overheated so departed to go to her daughter’s apartment, and is feeling much better.”

Clinton was seen a few hours later leaving her daughter’s apartment. She smiled and waved as she left Chelsea’s apartment at about 11: 45 a.m., saying she was “feeling great” and that “it was a beautiful day in New York.”

“[She] felt overheated so departed to go to her daughter’s apartment.”

Here is Hillary Clinton leaving Chelsea's apartment. (A little girl came up to give her a hug) pic.twitter.com/VreSXmT1Yh — Liz Kreutz (@ABCLiz) September 11, 2016

Witnesses also confirmed that temperatures were relatively high at Ground Zero at the time, about 80 degrees and that humidity was high.

It was uncertain whether the area where she had been standing during the ceremony was shaded.

The latest incident will further fuel rumors about Clinton’s health by her political opponents who had vowed to make her health a “major campaign issue.”

No sooner had the Clinton campaign said the Democratic presidential candidate had “overheated” than Fox News reported that some witnesses said her aides were trying to downplay the incident and that she appeared at the time to be in a worse condition than was admitted.

Clinton’s right-wing opponents have engaged in intense speculation about her health lately, and the Republican presidential candidate Donald Trump has also raised concerns about it.

But her doctors insisted she was in good health after recovering from surgery following a blood clot in 2012. Clinton’s personal doctor, Lisa Bardack, insisted she was “in excellent health and fit to serve as president of the United States.”

“To reiterate, Secretary Clinton is in excellent health and fit to serve as President of the United States.”

Latest incident will further fuel speculation about Hillary Clinton's health [Image via Marianne Campolongo/Shutterstock]

Clinton campaign reacted to questions, speculation and rumor-mongering about her health, describing it as “deranged conspiracy theories.”

“Back in October, the National Enquirer said I would be dead in six months,” Clinton told Jimmy Kimmel. “I don’t know why they are saying this. I think it is part of the wacky strategy — just say all these crazy things and maybe you can get some people to believe you.”

Some of her opponents had actually circulated fake medical reports. Photos and videos pushing various theories about her health surfaced online. One photo purportedly showed her stumbling as she climbed a flight of stairs.

Right wing news sites and blogs attributed her stumbling to ill-health.

A video showing Clinton bobbing her head in response to media reporters’ questions was also the subject of intense speculation, with some claiming she exhibited symptoms of Parkinson’s disease in the video.

Dr. Drew Pinsky also claimed on his HLN show that Clinton was suffering from brain damage and other serious ailments.

[Image via Evan El-Amin/Shutterstock]