The actor, who is currently in Texas for his world tour Unforgettable, posted a 'Happy Birthday To Me' note on his blog.
'August 2, 1982! It is the day in Breach Candy Hospital, Mumbai, after the 'Coolie' accident that I lived again. A time when the prayers of hundreds of well-wishers and fans brought me back to life, " he wrote.
'This is a debt that I shall never be able to pay back. I am with you today because of those prayers. Prayers from so many, whom I never knew, never met and probably never shall. I thank you, ' he added.
While filming 'Coolie' in 1982 Amitabh seriously injured his intestines during a fight scene with co-actor Puneet Issar.
He was taken to the hospital and was operated upon. He remained critically ill for many months.
The accident received wide coverage and a Bachchan hysteria gripped the country. Hordes of fans thronged temples, praying for his well-being.
More than two decades later, communicating to his fans through the blog, the actor said: 'I wish to thank through this wonderful medium the gracious congratulations from those (fans) on the 100th day of my blog.'
'It has been a wonderful journey for me - educative, revealing and emotional. It has given me the opportunity to reach out to you in a manner I would perhaps have never envisaged, ' he posted.