The Aarakshan star is in Sydney to shoot for the Hollywood project alongside Leonardo DiCaprio and Tobey Maguire.
Bachchan Tweeted: "The shoot for The Great Gatsby for Baz Luhrmann! Butterflies as large and as huge as the Transformers monsters in the film that I breezed through on the flight.
"Apprehensions, as fearful as the raging thunder and lightning storm that broke over the Mumbai skyline just prior to my departure last night...
"Starting work tomorrow morning... new environs, new systems, new colleagues, new set up... new nerves and fresh butterflies!!"
The Great Gatsby is a $125m 3D adaptation of the classic F. Scott Fitzgerald novel in which Bachchan plays the role of gambler Meyer Wolfsheim, a mysterious figure who helps Jay Gatsby accumulate his fortune.
Baz Luhrmann has said that he is "honoured" to be collaborating with Amitabh Bachchan on The Great Gatsby.
The film is set for release in 2012.