Maurice Gibb in Critical Condition
Doctors had been operating on Gibb, 53, in order to remove an intestinal blockage after he collapsed at his Florida home, but he suffered a heart attack during the surgery.
It was said that Gibb was complaining of stomach pains on Thursday morning.
His wife, Yvonne, and his two children are reportedly at his side awaiting updates, which Maurice's twin brother, Robin Gibb, has been forwarding to the BBC.
Robin said Maurice had been squeezing his daughter's hand and is "much improved," but that the next 24 hours would be "crucial," the news organization reports.
Fans also have been gathering outside the hospital.
The musician, along with Robin and older brother Barry, was one of the biggest pop stars of the 1970s. (The youngest brother, Andy, died of a heart attack in 1988 at the age of 30, following years of alcohol and drug problems. Maurice has also had alcohol problems in the past.)
The Bee Gees' soundtrack to the 1977 movie "Saturday Night Fever," starring a young John Travolta in his first leading role, is credited with launching the worldwide disco craze.