JK Rowling slammed US newspapers for publishing reviews of ‘Harry Potter and the Deathly Hallows’ two days before the book comes out.
The New York Times is among those to reveal a succession of plot spoilers for the seventh and final instalment.
A US online retailer shipped up to 1,200 copies of the book to customers on Tuesday - breaking the strict embargo of midnight tomorrow.
The internet is also awash with copies of pages supposedly scanned from the book.
A spokeswoman for publisher Bloomsbury said the reviews 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 midnight on Saturday July 21 is being enforced unflinchingly and without exception by the publishers," it said.
