Harper Lee's 'Go Set a Watchman' hits the shelves

American novelist Harper Lee's eagerly awaited novel "Go Set a Watchman" hit the shelves across the globe on Tuesday, media reported.

Lee, who is now 89 and living in a nursing home in Monroeville, Alabama, originally wrote the book in 1957.

The book is Amazon's most pre-ordered book since the final Harry Potter, BBC said in its report.

The book is set 20 years after the events of Lee's 1960 Pulitzer Prize-winning novel "To Kill a Mockingbird".

The existence of "Go Set a Watchman" was revealed in February. The opening chapter of the novel was published for the first time on Friday, and many early reviews revealed that in later years Atticus Finch had in fact become "a bigot".

"This story is of the toppling of idols," wrote Sam Sacks in the Wall Street Journal, adding that it was "a distressing book, one that delivers a startling rebuttal to the shining idealism of "To Kill a Mockingbird".

"For the millions who hold that novel dear, "Go Set a Watchman" will be a test of their tolerance and capacity for forgiveness," he said.

The New York Times said the revelation could "reshape Ms Lee's legacy" and made for "disturbing reading".

"If the text now published had been the one released in 1960, it would almost certainly not have achieved the same greatness," Mark Lawson wrote for The Guardian.

"It feels like a sequel. But really, it's more like a ghost: the spectre of Lee's restless, ardent thoughts in progress," Gaby Wood wrote for The Telegraph giving two stars to the book.