Vienna - Three-time Formula One champion Niki Lauda is in a "very satisfying" state four days after undergoing an emergency lung transplant following an infection, Vienna's general hospital said on Monday.

"Already 24 hours after surgery Mr Lauda could be extubated, was spontaneously breathing and had full consciousness," the hospital said in a statement.

"During the following days his condition has further improved continuously and all organs are functioning well," it went on.

Lauda, 69, had cut short his holiday in Ibiza at the end of July and returned to Vienna for treatment after developing a lung infection.

He was made a priority for a transplant after having to be put on an artificial lung.

The poisonous gases inhaled during his infamous 1976 accident - where rescuers took almost a minute to pull him from his burning car - have caused a steady decline in the strength of his lungs.

Dr Walter Klepetko, who performed the transplant, told the Oesterreich newspaper that Lauda would have to wait several weeks before leaving hospital but that barring any complications he should eventually "again be able to fly, work and take part in sport as he did before".

Usually a regular presence in the Grand Prix paddocks around the world with Mercedes, where he's non-executive chairman, Lauda had missed the Hockenheim race on July 22 and the Hungary event the week after because of his illness.

Lauda is also very active in aviation - in January he bought back his old airline Niki, renaming it LaudaMotion but going on to sell a majority stake to Irish low-cost operator Ryanair two months later.

According to Oesterreich, just before his operation he contacted Ryanair boss Michael O'Leary with a view to selling his remaining stake in the business and reducing his workload.

Crowned world champion for the first time in 1975, Lauda cheated death the following year in a horror crash at the German Grand Prix at the Nurburgring which left him with severe burns.

Despite that, he would still capture further world titles in 1977 and 1984.

Lauda, who also required kidney transplants in 1997 and 2005, is the father of four children from two marriages - Lukas (39), Mathias (37) and eight-year-old twins Max and Mia.