Sir Elton John cut his Auckland show on Sunday short, nearly collapsing on stage due to what he called "walking pneumonia".

The global superstar had previously told the Mt Smart audience he'd been diagnosed with the condition on Sunday morning, and eventually had to end the show after hammering out 16 of the 25 songs on his set list.

"I played and sang my heart out, until my voice could sing no more," John said later to fans, thanking them for their support and saying he was upset that he could not complete the show.

Walking pneumonia, while not actually a medical term, is not as severe as general pneumonia, which is a serious lung infection that happens when the air sacs in a lung or lungs fill with fluid or pus making it harder to breathe and without treatment, can be life-threatening.

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According to the Centers for Disease Control and Prevention, walking pneumonia is an infection caused by a type of "atypical" bacteria, that commonly causes mild infections of the respiratory system.

Symptoms include "being tired and having a sore throat, fever, and cough", according to the Centers for Disease Control and Prevention.

Experts say people with walking pneumonia are generally not sick enough to need to stay in bed.

Asthma and Respiratory Foundation NZ medical director Dr Stuart Jones said walking pneumonia was not a term generally used in hospitals, where most people with pneumonia "are not walking".

"It is not a regularly-used term, but I think it has been used to describe milder forms of community-acquired pneumonia - it is quite a non-specific diagnosis and is at a level that does not require hospitalisation."

John's promoter announced the next Auckland show has been rescheduled from tonight to Wednesday to allow the performer an extra day to recover.

Jones said it was difficult to say how long one could take to recover without knowing the extent of John's condition, but in cases of pneumonia people generally took one to two weeks to recover, and often even longer.

"One day does seem a short time."

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Microplasma or viral infections were quite common in the community, and the best prevention was practising good hand hygiene, and maintaining a healthy diet and lifestyle.

However, older people were more susceptible, and after touring since September 2018 it was likely stress could be a factor in John's condition.

"With constant stress on your body you are more likely to pick these sorts of infections up and take longer to recover," Jones said.