Prime Minister John Key has sympathy for US presidential candidate Hillary Clinton's recent ill health after his own fainting spell in 2013, which he put down to the "rough and tumble of the job".

Clinton's health has become one of the big issues of the US election campaign after she became unwell during a memorial for the September 11 attacks and news she had been diagnosed with pneumonia.

Key said he could not speak about Clinton's health but his own fainting spell in 2013 was "completely out of the blue".

That was in January 2013 when Key fainted in a Christchurch restaurant on the eve of flying to the Antarctic.


Key's faint put his trip in jeopardy but after a two-hour stint at hospital and checks from three specialists he was cleared to travel.

Key said it had never happened again.

"Maybe it's just the rough and tumble of the job."

He said he had a "full bank of tests" every year - the most recent ended last week. "It's in perfect nick.

"They probably do a bit more than what would necessarily be the case for my age, but I take the view it's good to be cautious about these things. They've run everything on me from looking fully at my heart to making sure they're keeping on top of every other test."

Asked if he was told he had the health of a man younger than his years, he said: "I wish they did. They usually tell me to lose two kilos."

Labour leader Andrew Little said he did not believe he had ever fainted. "My blood runs to my head in a very consistent fashion."

He also had regular health checks, partly because of his history with prostate cancer about seven years ago. "[I'm the] picture of health."

The 2013 faint was not Key's only brush with illness in public.

In September that year, Key came over queasy in a planter box outside an Irish pub in New York while on his way to a lunch at the UN.

He had to be whisked to the bathrooms inside by his protection squad.

He emerged still green but rallied and continued on to the luncheon.

He later said it was a "short and sharp" period of illness, possibly caused by something he ate.

That was just hours after he had landed in New York after travelling in the UK and France.

Having once said his worst nightmare was falling over in front of the cameras, in 2009 Key fell down some stairs at a function and broke his arm. That was a Chinese New Year function to welcome in the Year of the Ox. Key was born in 1961 - another Year of the Ox.