Exclusive Video footage :Hillary Clinton collapsing at 9/11 memorial

Former U.S. Secretary of State Hillary Clinton, the Democratic Party's presidential nominee, abruptly left the 9/11 ceremony in Manhattan after she "felt overheated", her campaign says. She stumbled as she tried to get into a van. (more) 

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The incident happened on Sunday morning as Clinton attended the annual ceremony at Ground Zero for the 15th anniversary of the September 11 attacks. After about 1.5 hour, she "felt overheated" and left the ceremony to go to her daughter's apartment, campaign spokesman Nick Merrill said.

The incident happened in an area that is off-limits to the press, but video later emerged from a bystander who was filming as Clinton waited for her van. It shows Clinton leaning against a pole while surrounded by aides, and she stumbles and required help as she is carried into the vehicle.

As the video emerged, Clinton emerged from her daughter's apartment, waving to reporters and saying she was feeling great.

Clinton's campaign had remained silent for about an hour as speculation intensified about her abrupt departure. "Clinton left the 9/11 ceremony 30+ mins ago but press pool was not told to where. Aides now not responding to any [questions] about her whereabouts," ABC News journalist Liz Kreutz said.

Clinton, who previously served as a senator from New York, was attending the annual ceremony at Ground Zero for the 15th anniversary of the September 11 attacks. Her Republican opponent, Donald Trump, also attended the event.

Speculation of ill health have plagued Clinton's campaign over the past few months, but the campaign has rejected those as unfounded rumors, and her personal doctor said she had no health issues. Sunday's episode is likely to add to the speculation.