Hillary Clinton diagnosed with pneumonia

US Democratic presidential candidate Hillary Clinton has been treated for pneumonia, her doctor says, after she was taken ill at a 9/11 ceremony.

Dr Lisa Bardack said she was diagnosed with pneumonia on Friday and given antibiotics, but had become dehydrated at the New York event.

The doctor's statement said she was now re-hydrated and "recovering nicely", BBC reports.

But a campaign official said she has cancelled a campaign trip to California due to the illness.

She was due to leave for California on Monday morning for a two-day trip that included fundraisers and a speech on the economy.

"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," Dr Bardack's statement said.

"She was put on antibiotics, and advised to rest and modify her schedule," it went on.

On Sunday, video showed her being supported by aides as they put her into her van after she left the 9/11 ceremony in New York early.