Excitement surrounds 'Go Set a Watchman' book release

The book is set 20 years after the events of Lee's 1960 Pulitzer Prize-winning novel To Kill a Mockingbird, but was actually written beforehand.

Thanks to pre-orders, it has been the number one bestseller at online retailer Amazon for months, and publisher HarperCollins has ordered a first print run of two million copies. Lee's only previous novel, "To Kill a Mockingbird," is considered a 20th century masterpiece that defined racial injustice in the Depression-era South and became standard reading in classrooms.

Published in 1960, it was translated into more than 40 languages and adapted into an Oscar-winning film starring Gregory Peck.

The story of racism and injustice in the fictional town of Maycomb in the American South went on to sell 40 million copies and be studied in schools around the world.

HarperCollins says "Watchman" has been published exactly as it was written, "without editorial intervention," at Lee's behest.

The book is a coming-of-age story that explores "racism and changing attitudes in the South during the 1950s in a bold and unflinching way," it said in a statement.

"By confronting these challenging and complex issues at the height of the Civil Rights movement, the young Harper Lee demonstrated an honesty and bravery that makes this work both a powerful document of its time and a compelling piece of literature."

Some of those who queued said that the new book portrays the honourable lawyer Atticus Finch as racist.

The global release of "Go Set a Watchman" has been feted as one of the biggest literary events in years.