More than 100,000 copies of Harry Potter and the Deathly Hallows were pre-ordered on Amazon's web sites in the first two days and, according to the retailer, no other book has sold so quickly before a launch.
Amazon head of books Christopher North said: 'It is set to be our biggest-selling book ever.'
There were rumours that Harry Potter author JK Rowling would release the seventh instalment in the series as an e-book, but this has been refuted because of concerns about piracy.
The book will be released in stores on July 21, but is predicted to sell more than 400,000 copies before it even hits the shops.
The first six books sold more than 325 million copies.