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.
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.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies