JK Rowling criticised American newspapers today for publishing reviews of Harry Potter and the Deathly Hallows two days before the final book in her wildly successful series comes out.

The New York Times, which says it bought the book from a city store on Wednesday, is among those to review the seventh and final instalment.

Its chief reviewer, Michiko Kakutani, does not reveal which characters are killed off, despite fevered speculation among fans that Harry himself could be among them - but she does reveal that six characters meet their end.

Ms Kakutani describes the final pages of the book as "a big-screen, heart-racing, bone-chilling confrontation" and adds it contains "an epilogue that clearly lays out people’s fates".

She adds: "Getting to the finish line is not seamless — the last part of Harry Potter and the Deathly Hallows, the seventh and final book in the series, has some lumpy passages of exposition and a couple of clunky detours — but the overall conclusion and its determination of the main characters’ story lines possess a convincing inevitability that make some of the prepublication speculation seem curiously blinkered in retrospect."

An American online retailer mistakenly shipped up to 1,200 copies of the book to customers on Tuesday - breaking the strict embargo of midnight tomorrow and making a mockery of the tight security surrounding the release. It also prompted legal action from the book's US publisher.

The internet is also awash with copies of pages supposedly scanned from the book and a spokeswoman for its UK publisher, Bloomsbury, even suggested today that reviews already published may be based on fake copies.

In a statement, Rowling said: "I am staggered that some American newspapers have decided to publish purported spoilers in the form of reviews in complete disregard of the wishes of literally millions of readers, particularly children, who wanted to reach Harry’s final destination by themselves, in their own time.

"I am incredibly grateful to all those newspapers, booksellers and others who have chosen not to attempt to spoil Harry’s last adventure for fans."

Bloomsbury was "extremely dismayed" to learn that some copies of the book have already been sent out.

"The release date and time embargo of 0001 BST on Saturday July 21 is being enforced unflinchingly and without exception by the publishers," it said.

The books officially go on sale in the United States, Canada and Mexico at midnight on Friday - a separate embargo to the rest of the world.

The furore threatens to overshadow the release of the book, eagerly awaited by fans around the world, some of whom are already queuing,

Those outside Waterstone’s on Piccadilly, in London's West End, included Laura Halinen, 23, from Finland who was dressed as a wizard and said she had come because this was "the biggest Harry Potter party in Europe and perhaps the world".

Rowling is hosting an overnight reading and signing with hundreds of fans at the Natural History Museum, while hundreds of bookshops are hosting after-hours parties to which fans are likely to flock.

"The first night outside was horrible - I thought it would be a fun way to get back to nature but it was not at all," added Amber de Jager, 19, from the Netherlands, who has been queuing outside Waterstone’s since yesterday.

"Fortunately, we reserved some hotel rooms nearby and I will take a shower and rest during the day."

The Potter books have sold 325 million copies internationally and are translated into 64 languages. Rowling, who wrote the first one as a single mother receiving state benefits, has made an estimated £500 million from the works since the first one appeared in 1997.

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