A long-awaited sequel to "Shantaram" went on sale on Tuesday, 12 years after the novel about an escaped Australian convict in India became a huge backpacker hit, selling four million copies worldwide.

It took the Australian author Gregory David Roberts 10 years to write "The Mountain Shadow", which picks up the story two years after "Shantaram" ends.

Roberts' first novel became an international sensation when it was released in 2003 for its colourful depiction of the Indian city of Mumbai.

It centres on the life of a convicted Australian bank robber and heroin addict who escapes jail and flees to India, becoming embroiled in the Mumbai underworld.

"Shantaram" acquired a cult following, with television chat show queen Oprah Winfrey describing it as one of her favourite novels on a visit to India in 2012.

It was given an added air of mystique by claims from Roberts that elements of it were based on real life events and the 900-page doorstopper became a favourite amongst backpackers.

It sees the main protagonist, "Lin" set up a health clinic in a slum, fall in love, and fight with the Mujahideen in Afghanistan.

Publisher Little, Brown UK has said it took Roberts 10 years to complete the sequel, and fans took to Twitter to express their excitement.

"Today's the day! Been waiting for this to be released since I first read Shantaram 3 years ago," Wes Cartlidge tweeted.