George Michael has been forced to cancel tour dates due to illness.

The 48-year-old singer fell ill with pneumonia in Vienna, Austria this week.

George has been battling a chest infection for several weeks and the condition quickly degenerated.

At the advice of medical personnel, all dates on George's current Symphonica world concert tour must be postponed, British newspaper the Sun reports.

"To ensure his complete well-being, George Michael's doctors have advised that he cannot perform the rest of his Symphonica tour and that he instead takes a full and complete rest," read a statement released by George's publicity team.

The Austrian doctors who are currently treating George note the seriousness of his sickness.

"George Michael has severe community acquired pneumonia and is being treated as an inpatient. His condition has stabilised and he is responding to treatment," the doctors said in a release.

"From the current point of view, the time until recovery cannot be estimated, but he will not be able to perform the rest of the tour. Besides medical treatment, complete rest and peace and quiet are mandatory."

A spokesperson for George assured concertgoers that all postponed performances will be rescheduled.

This is the second time George has been hit by health problems on his Symphonica world tour.

Last month, he was forced to cancel a sell-out show in London after his spokesperson said he was suffering from a viral infection.

The tour kicked off in Prague, Czech Republic, in August.