His agent David Hahn expressed great shock and revealed that Reid had recently undergone a medical examination which had given him a "clean bill of health".
"Mike was a very, very, very funny man," said Hahn. "He would see the funny side of every situation, no matter how black it was.
"Even now I am sure he is laughing ... He always had time for the man on the street. He's going to be sadly missed."
Close friend of the actor and fellow comedian Frank Carson, speaking from Spain after hearing the news, said it was "absolutely devastating".
Born in Hackney, east London, Reid began his career as a stuntman working on films such as "Chitty Chitty Bang Bang", "Those Magnificent Men In Their Flying Machines" and "Spartacus". He was also a stunt double for Roger Moore in "The Saint".
He started his career as a stand-up comedian in the 1960s and got his first big break on the popular TV show "The Comedians" in 1973. But real success came knocking when he was given the part of EastEnder Frank Butcher, quickly turning it into one of the show's most popular characters.
After taking a lengthy time away from the part due to stress in 2000, Reid returned to the role and made his last appearence as Frank in December 2005.
He also went on to appear in Guy Ritchie's gangster movie "Snatch".
John Yorke, controller of BBC Drama Series, paid tribute to the actor, saying: "Frank Butcher was one of a select group of truly great EastEnders' characters and the skill with which Mike Reid played him made him one of the most popular and well-loved of all.
"Frank could break your heart and make you prostrate with laughter - often at the same time.
"Mike's genius was to capture the heart of that flawed dreamer and make generations of viewers love him."
Fellow entertainer Russ Abbot said Reid was a great story-teller who had a great sense of comic timing.
"There certain comedians who do one-liners but Mike was a story-teller and a great deliverer," he said.
Actress Pam St Clement, who played Reid's Eastenders wife, Pat, said: "I'm sorry to lose such a dear friend and colleague. Mike, as a person and character, seemed indestructible."
©AFP