By, Claudio Lavanga, NBC News

ROME, Italy - James Gandolfini's teenage son called for help after discovering his father collapsed in a bathroom, according to the manager of the Italian hotel where the "The Sopranos" star was staying. The Emmy-winning actor was later pronounced dead aged 51.

Gandolfini, who rose to fame as mob boss Tony Soprano on the hit HBO show, was still alive when the ambulance arrived, according to Antonio D'amore, who runs the Hotel Boscolo in Rome.

SLIDESHOW | Actor James Gandolfini's roles

Gandolfini suffered a suspected heart attack in the bathroom of his hotel room at about 10 p.m. local (4 p.m. ET) Wednesday, according to D'amore.

He said Gandolfini's son, Michael, was with him in the room and called for help. Hotel staff rushed to the room and found the actor on the bathroom floor, D'amore said.

Workers tried to resuscitate him but he was later pronounced dead at the Policlinico Umberto I hospital, which is about a three-minute drive from the hotel.

Gandolfini and his family were visiting Rome prior to his scheduled appearance on Saturday as guest of honor at the Taormina Film Festival in Sicily.

"He was a genius," said "Sopranos" creator David Chase. "Anyone who saw him even in the smallest of his performances knows that. He is one of the greatest actors of this or any time."

Gandolfini won critical acclaim, three Emmy Awards and three Screen Actors Guild awards for playing Tony Soprano from 1999-2007.

"We're all in shock and feeling immeasurable sadness at the loss of a beloved member of our family," HBO said in a statement. "He was a special man, a great talent, but more importantly a gentle and loving person who treated everyone no matter their title or position with equal respect. He touched so many of us over the years with his humor, his warmth and his humility. Our hearts go out to his wife and children during this terrible time. He will be deeply missed by all of us."

Although a New Jersey native, Gandolfini didn't expect to land the role of Tony Soprano. "I thought that they would hire some good-looking guy, not George Clooney but some Italian George Clooney, and that would be that," he told Vanity Fair in 2012.

But instead, it was Gandolfini who got the nod, and he made viewers care about a mob boss who could order the murder of a family member one minute and turn around and tenderly feed the ducks that swam in his estate's swimming pool the next.

"I think you cared about Tony because David was smart enough to write the Greek chorus, through (Soprano's psychiatrist) Dr. Melfi," Gandolfini said. "So you sat there and you got to see his motives, what he was thinking, what he was trying to do, what he was trying to fix, what he was trying to become. And then you saw it didn't really work out the way he wanted it to."

Actress Lorraine Bracco, who played Melfi, said in a statement,"We lost a giant today. I am utterly heartbroken."'s Gael Fashingbauer Cooper and NBC News' Alastair Jamieson contributed to this report.