Emmy Award-winning actor James Gandolfini, known to millions as Tony Soprano, has died after a suspected heart attack at the age of 51 while on holiday in Italy.

Gandolfini, who shot to fame on HBO mafia drama The Sopranos, was reportedly traveling in Rome, where he was on vacation with his son Michael, and was scheduled to attend the 59th Taormina Film Festival in Sicily.

He is survived by his second wife, former model Deborah Lin, and two children - Michael, from his first marriage to Marcy Wudarsk, and nine-month-old daughter Liliana Ruth.

Actor and friend Gilles Marini took to Facebook to pay tribute to Gandolfini, recalling their final conversation.

"I am heartbroken. My bud James Gandolfini just died. Last Saturday he told me at our kids graduation that he was so happy to go with his son to Italy. A boy trip!" Marini wrote.

"It was an honor to have met this man, such a great Dad! I spent so much time with James' son teaching him soccer. I feel for that kid it must be so hard right now for little Micheal . Guys say a prayer for him and his family. This is going to be very difficult time for them. I am so so sad! RIP Brother you'll be missed!"

Sopranos creator David Chase also described him as one of the greatest of all time.

"He was a genius. Anyone who saw him even in the smallest of his performances knows that," he said, "He is one of the greatest actors of this or any time. A great deal of that genius resided in those sad eyes. I remember telling him many times, 'You don't get it. You're like Mozart" There would be silence at the other end of the phone.

"For Deborah and Michael and Liliana this is crushing. And it's bad for the rest of the world. He wasn't easy sometimes. But he was my partner, he was my brother in ways I can't explain and never will be able to explain."