A video shot by a Twitter user showing US Democratic nominee Hillary Clinton stumbling and falling as she exited the 9/11 event early has raised questions about her health, ahead of the US Presidential polls. Hours later, her doctors said she had pneumonia, according to CNN.

Clinton was diagnosed on Friday with pneumonia, and "was put on antibiotics, and advised to rest and modify her schedule," Dr. Lisa Bardack said in a statement, reported CNN.

"While at this morning's event, she became overheated and dehydrated. I have just examined her and she is now re-hydrated and recovering nicely," said Bardack.

After the 9/11 event, the Democratic nominee traveled to her daughter's nearby apartment and her office said that she felt "overheated." Clinton appeared to faint as she was leaving, said media reports.

Leaving her daughter's apartment later that day, Clinton told reporters she was "feeling great."

"It's a beautiful day in New York," she added.