It has been called the most anticipated book since the final in the Harry Potter series.

The Lost Symbol, the sequel to American author Dan Brown's bestseller The Da Vinci Code , will have its worldwide release on Tuesday at 9am Sydney time.

Its first print run of 6.5 million copies is the largest in publisher Random House's history.

It is rumoured that the secretive worldwide fraternity, the Freemasons, are at the heart of the story, with its narrative said to take place within a 12-hour period.

The independent Sydney bookstore Abbey's Bookshop is keeping its 400 copies of the book under ''lock and key'' until its 9am release on Tuesday, according to its website.

The bookstore's deputy manager, Christian Hummelshoj, expected there would be great demand for the sequel, based on pre-orders.

''We've certainly got quite a number reserved already and we're expecting a lot of people to see other people reading it on the train and come in,'' he said.

''[Brown's] previous ones sold quite well, so this one should as well.''

Members of the United Grand Lodge of Freemasons of NSW and the ACT were in Newcastle for a state conference and could not be contacted yesterday, according to the NSW Freemasons Association secretary, Garry Sayed.

However, the Australian chapter recently issued a press release to reporters, which said: ''The book's publisher promises a thriller based on the role of Freemasons in US history and politics, a subject charged with sufficient mystery to provoke widespread interest in the Masonic Craft.

''Freemasonry is not a secret society. It has long been misunderstood.''

Brown says he has been working on the book for the last five years, although he did have to take time out to defend The Da Vinci Code successfully in the High Court in London against a plagiarism action brought by the authors of another book from his own publishers, The Holy Blood and the Holy Grail.

''This novel has been a strange and wonderful journey,'' Brown said in a message on his website.

Despite savage reviews of the clunky style and tortuous religious conspiracy plot of the 2003 The Da Vinci Code, the book became a worldwide phenomenon, with more than 81 million copies in print. The film got even worse reviews and equally stunning box-office results, taking $758 million to date.