Hillary Clinton has decided to cancel her campaign trip to California after being diagnosed with pneumonia.

The Democratic presidential nominee was taken ill yesterday at a 9/11 memorial ceremony in New York City and was seen stumbling as she left the event early.

Hillary Clinton’s team initially said she was “overheated”, later revealing she had been diagnosed on September 9 with pneumonia.

Her doctor said she was now re-hydrated and “recovering nicely”.

Hillary Clinton was due to leave for California on September 12 for a two-day trip that included fundraisers, a speech on the economy, and an appearance on the Ellen DeGeneres Show.

Dr. Lisa Bardack, Hillary Clinton’s personal physician, said: “Secretary Clinton has been experiencing a cough related to allergies. On Friday, during follow-up evaluation of her prolonged cough, she was diagnosed with pneumonia. She was put on antibiotics, and advised to rest and modify her schedule.”

On September 11, video showed Hillary Clinton being supported by aides as she entered a van to leave the 9/11 ceremony after an hour and 30 minutes.

Hillary Clinton was taken to her daughter’s flat in New York’s Flatiron building and re-emerged later in the day, telling reporters: “I’m feeling great. It’s a beautiful day in New York.”

She then left for her home in Chappaqua, New York.

Hilalry Clinton’s Republican opponents have queried her physical fitness. She suffered coughing fit last week at a campaign event in Cleveland, Ohio which fuelled speculation about her condition.

Last month, Dr. Lisa Bardack said in a letter that Hillary Clinton was “in excellent health and fit to serve as president of the United States”. She made a full recovery from surgery she underwent in 2012 for a blood clot, the doctor added.

However, Republican rival Donald Trump has repeatedly suggested Hillary Clinton is unfit, telling supporters last month she “lacks the mental and physical stamina” to serve as president.

Hillary Clinton’s campaign has accused opponents of pushing a “deranged conspiracy about Clinton’s health”.

The Democratic candidate is 68 while her Republican opponent is 70.

Donald Trump has not published his medical records. Instead the New York businessman released a note, in which his doctor declared that he would be “the healthiest individual ever elected to the presidency”.

Donald Trump’s team has not yet made any comment on Hillary Clinton’s pneumonia diagnosis.