Shocked fans at the sell-out concert at the Hordern Pavilion were urged to leave the auditorium by Buffett's Australian tour manager Michael Chugg as the 64-year-old entertainer lay on the floor in front of the first row of seating waiting for paramedics and an ambulance to arrive.
He was rushed to Sydney's St Vincent's Hospital, in Darlinghurst, thirty minutes after the accident.
Neither Chugg nor his assistant David Pope would comment on Buffett's condition at the scene but an audience member said it appeared the entertainer had struck his head and was bleeding as he lay on the floor.
Chugg took the stage and insisted anxious fans leave immediately with security hustling the audience outside before the ambulance arrived.
Several fans said they felt that some statement could have been made about Buffett's condition before they were pushed outside.
After Buffett fell it appeared as if security men were arguing with a large man who had been at the front of the audience.
Audience member Dan Bateman, 30, told The Daily Telegraph Buffett fell face first off the stage.
"We were in the 10th row and it looked like he did a massive face plant after his encore and pretty much didn't get up,'' Mr Bateman, from Cairns, said.
"We were told to leave the premises. No one really wanted to leave because everyone was anxious to know if he survived the fall. Everyone was pretty horrified.''
Buffett had performed at the Opera House for three sell-out shows before last night's Australia Day performance which was a late add-on to accomodate fans unable to get tickets to the performances earlier in the week.
His last show was full of references to Australia and Australia Day, and, after apologising for not appearing in the country for 20 years, he said he and his Coral Reefer Band would return in 2012.
