Hillary Clinton has been diagnosed with pneumonia, seemingly answering the recent nagging questions over her health.

Ms Clinton’s doctor says she is “recovering nicely”, soon after the Democratic presidential candidate had to leave a September 11 memorial ceremony in New York after becoming overheated and seeming to almost faint.

The moment was caught on video and posted on YouTube:

https://www.youtube.com/watch?v=lz9UNDR4B9Q

Clinton said she was “feeling great” when leaving her daughter Chelsea’s home in Manhattan, where she was taken after departing the memorial service.

Clinton left the event after about 90 minutes while it was still underway, Nick Merrill, a Clinton spokesman, said.

He gave no further details about her condition.

As the event began on Sunday at the site of the World Trade Center that was attacked by two hijacked airliners 15 years ago, there was patchy sunlight, with temperatures at about 80 degrees Fahrenheit (26.6 Celsius).

Democratic Representative Joe Crowley of New York, a Clinton supporter who attended the event, told MSNBC television that it was “stifling” during the ceremony.

After some US media reported she had fallen ill, reporters travelling with the candidate did not get an immediate response from the campaign to questions about her whereabouts and her health.

About 90 minutes elapsed before the campaign issued a statement.

NEW: statement from @HillaryClinton campaign spox. She "felt overheated" and left ceremony; went to Chelsea's apt. pic.twitter.com/tYaTEDFMhz

— Hallie Jackson (@HallieJackson) September 11, 2016

Republican presidential candidate Donald Trump repeatedly has raised questions about Clinton’s health and whether she had the “stamina” to serve as president.

In December 2012, Clinton, 68, suffered a concussion and shortly afterward developed a blood clot.

In a letter released by her doctor in July, Clinton was described as being in “excellent health” and “fit to serve” in the White House.

Clinton’s speech at a campaign rally earlier this month in Cleveland was interrupted by a coughing spell.

During the speech, she quipped, “Every time I think about Trump I get allergic”. She then resumed her speech.

But the episode fuelled speculation from conservative political quarters about her health.

https://twitter.com/TrumpWhiteHouse/status/775032764081004544

Trump supporters have been tweeting unsubstantiated theories regarding Clinton’s health under the hashtag #HillarysHealth.

And they didn’t hesitate to capitalise on this incident.

#ClintonCollapse

Eventually ALL will understand this is NOT about a conspiracy its about the safety of America!https://t.co/mSJXb2ye2N

— Deplorable Rochelle (@SecretAZ12) September 11, 2016

Here is another video. Watch her head & feet closely. @HillaryClinton had a seizure. She is twitching not fainting. https://t.co/4cnVtOofEU

— VoiceOfReason🇺🇸 (@Voix_Of_Reason) September 11, 2016