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Hillary Clinton has been rushed away from the 9/11 memorial service in New York as she was feeling unwell.
A video shows the Democrat stumbling and being carried into a van, with aides and security guards on either side.
As she is being helped towards the vehicle, she appears to sink towards the ground, and her team gather closely around her to help her back up.
Her campaign said in a statement that Ms Clinton became "overheated" and left the service early.
Shortly afterwards Ms Clinton emerged from her daughter Chelsea's apartment in Manhattan. A little girl approached her and she was filmed hugging the girl, before smiling and waving to reporters as she walked away.
The news comes shortly after right-wing commentators including Donald Trump accused her of being unfit to be president.
Fox News anchor Sean Hannity, who advises Mr Trump, recently questioned the candidate's health, pointing out her "blinking" and exaggerated head movements as she spoke to reporters.
Show all 30 1 /30In pictures: Hillary Clinton's 2016 presidential bid In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 11/09/2016: Hillary Clinton waves to the press as she leaves her daughter's apartment building after resting in New York. Clinton departed from a remembrance ceremony on the 15th anniversary of the 9/11 attacks after feeling "overheated," but was later doing "much better," her campaign said
AFP/Getty Images
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 25/08/2016: Hillary Clinton speaks at a campaign event in Reno, Nevada
AFP
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 27/07/2016: US President Barack Obama and Democratic presidential nominee Hillary Clinton embrace on stage during Day 3 of the Democratic National Convention at the Wells Fargo Center in Philadelphia, Pennsylvania
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 11/07/2016: Bernie Sanders officially endorsed Hillary Clinton, saying his progressive vision for ‘a transformed America’ would be ’best served by the defeat of Donald Trump’
Reuters
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 26/06/2016: New York Governor Andrew Cuomo, former Secretary of State and Democratic Presidential candidate Hillary Clinton, Al Sharpton and New York mayor Bill de Blasio march during the New York City Pride March in New York City
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 7/06/2016: Democratic presidential candidate Hillary Clinton gestures as she greets supporters at a presidential primary election night rally in New York
AP
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 26/05/2016: A supporter of democratic presidential candidate former Secretary of State Hillary Clinton holds up a shirt during a campaign event in San Francisco, California
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 26/04/2016: Hillary Clinton embraces her husband, former President Bill Clinton, at a primary night campaign event in Philadelphia, Pennsylvania. Early results indicated Clinton would win Pennsylvania's presidential primary
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 8/03/2016: Hillary Clinton and Bernie Sanders during of the CNN Democratic Presidential candidates' debate, at the Whiting Auditorium in Flint, Michigan
EPA
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 3/03/2016: Singer Katy Perry raises arms with U.S. Democratic presidential candidate Hillary Clinton at the end of the Hillary Victory Fund "I'm With Her" benefit concert at Radio City Music Hall in the Manhattan borough of New York City
REUTERS
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 28/02/2016: Hillary Clinton delivered a victory speech in Columbia
AP
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 16/02/2016: Hillary Clinton speaks at a rally at Truckee Meadows Community College in Reno, Nevada
AP
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 9/02/2016 (L-R) Priyadharshini Shanthakumar, Hattie Hughes and Claudia Blair with Hillary Clinton campaigning in Derry, New Hampshire
Hattie Hughes
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 30/01/2016: Hillary Clinton is introduced by her daughter Chelsea while the two campaigned together at a 'Get Out The Vote" caucus' event at the Carrollton Inn in Carroll, Iowa
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 14/12/2015: Hillary Clinton speaks during the National Immigrant Integration Conference in New York City. During the speech Clinton announced her immigration proposals if elected president
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 9/11/2015: Hillary Clinton speaks on stage during a rally after filing paperwork for the New Hampshire primary at the State House in Concord, New Hampshire. Each candidate must file paperwork to be on the New Hampshire primary ballot, which will be held on 9 February 2016
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 22/10/2015: Hillary Clinton avoided major damage to her presidential campaign during a nearly 11-hour congressional hearing dominated by Republican criticism of her response to the Benghazi attacks
AFP
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 9/09/2015: Hillary Clinton takes part in a discussion after speaking about the Iran nuclear deal at the Brookings Institution in Washington. Clinton expressed firm support for the nuclear accord with Iran, calling it flawed but still strong. Clinton added that the agreement must be strictly enforced and said that if elected president next year, she would not hesitate to use military force if Iran fails to live up to its word and tries to develop a bomb
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 8/09/2015: Hillary Clinton does the "Nae Nae" dance move with DJ Stephen "Twitch" Boss (L) and television host Ellen DeGeneres (R) during a taping of "The Ellen DeGeneres show" in New York
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 26/08/2015: Hillary Clinton greets guests during a campaign event at Tabor Home Vineyards and Winery in Baldwin, Iowa. A recent poll has Clinton leading all other Democratic contenders in Iowa by about 30 percentage points
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 13/07/2015: Hillary Clinton poses for a selfie with a student outside the New School after speaking to outline economic vision in New York. Clinton promised to raise incomes of hardworking Americans and rein in excesses on Wall Street in the first major economic policy address of her 2016 campaign
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 15/06/2015: Hillary Clinton speaks during a forum on early childhood education at the YMCA of Strafford County in Rochester, New Hampshire. Clinton held a formal launch event in New York City, and is hitting the first in the nation primary state for the third time since announcing her candidacy in April
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 22/05/2015: Hillary Clinton tours the Smuttynose Brewery in Hampton, New Hampshire
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 23/04/15: Hillary Clinton addresses the Women in the World Conference in New York City
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 22/04/15: Hillary Clinton waves to college students as she leaves after speaking during the Hillary Rodham Clinton Award for Advancing Women in Peace and Security at Georgetown University in Washington
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In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 21/04/15: Hillary Clinton meets with audience members after speaking with students and faculty of New Hampshire Technical Institute in Concord, New Hampshire. The conversation revolved around higher education, manufacturing and women in the work force
Getty
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 13/04/15: “Loaded the van & set off for IA. Met a great family when we stopped this afternoon. Many more to come.” A picture of one family Hillary Clinton met on her road trip, which she tweeted
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 12/04/15: The building that will house Hillary Clinton's campaign headquarters, on the corner of Pierrepont and Clinton Streets in historic Brooklyn Heights, NY
Corbis
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 12/04/15: Some expect Hillary Clinton’s campaign to cost more than Barack Obama’s $1bn in 2012
EPA
In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 12/04/15: Hillary Clinton formally declares in a video that she will seek the Democratic Party’s presidential nomination for 2016, and says she wants to bring the benefits of the economic recovery to all Americans
AP
Ms Clinton, who recently released a letter detailing her health, suffered concussion in 2012 after a stomach virus, but she was reported as back to full health afterwards.
Mr Trump also claimed to have released a letter on his health, but the credibility of the letter was widely disputed.
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