He was hospitalised on Monday after a doctor was called to his suite at the Hotel imperial in Vienna's posh first district and diagnosed breathing difficulties.
He was taken by ambulance to the city's top Rudolfiner private hospital in the 19th district of the city, where a decision was taken to move him to the main general hospital - the AKH.
The hospital refused to say why the star was moved but it is believed it was decided that the singer's condition was so acute that it would be better if he was moved to the AKH - the biggest in Europe and where many of the continent's top medical experts are based because of the advanced facilities it offers for research as well as treatment.
The hospital has two skyscrapers, identified for navigating around the huge complex as the red tower and the green tower. He is currently in intensive care on the 13th floor of the red tower as a result of heart problems believed to be caused by the shortage of oxygen caused by his pneumonia.
On Thursday afternoon he was fitted into a special full-body bed designed to keep all the pressure off his lungs and to help them to function - so far without any sign of improvement.
Head doctor from the nearby Otto Wagner Hospital, Norbert Vetter, said that the reason a person with a lung problem was being treated in the cardiac unit probably lay in the fact that if there was a lung problem - and not enough oxygen being taken into the body - then that could affect the heart especially if the heart had already been damaged in some way. He added in the worst case the heart could cease to function.
AKH spokeswoman Karin Fehringer said: "We have no comment to make on this matter at the request of the patient."
But a hospital insider confirmed that the singer's condition had worsened. He said: "I have not seen him myself but cardiac specialists and internists are treating him round the clock." Internists specialise in treating adults with multi-system disease problems in hospitals.
A spokesman for his management team would only confirm his condition remained "bad".