Mandy Muldoon, the boy's mother, purchased 'Harry Potter and the Half-Blood Prince', the sixth instalment in J.K. Rowling's wildly popular series about a boy wizard, in a Kingston, New York drugstore.

The shop accidentally stocked the book on its shelves days ahead of the scheduled release, the US publisher Scholastic said.

But Kris Moran, director of publicity for trade at the publishing house, said she believed only one copy had been sold.

"As far as I know, he is the only one (in the United States)" who has the book, she said.

"I took it up to the clerk and said 'Is this really the book?'" Muldoon told the Poughkeepsie Journal newspaper, which ran a photo of her nine-year-old son, Sylum Mastropaolo, smiling broadly as he held the book.

The family said they later learned that the book was not being released until Saturday, and contacted the publisher, promising to return the treasured tome.

"The family contacted us. He's returning the book," the Scholastic spokesperson confirmed.

The Eckerd drugstore responded with a "no comment" but has given assurances that it pulled all of the books from the shelves within an hour of the mishap.

"I think they made a mistake," Moran said.

Earlier this week, a Canadian supermarket chain accidentally sold 14 copies of the book.

The grocer begged customers to return the books, but in the event that they refused, Canadian publisher Raincoast Book Distribution Ltd. sought an unprecedented injunction from a provincial court to keep the storyline a secret.

Justice Kristi Gill ordered the 14 customers not to talk about the book, copy it, sell it or read it until after midnight on Saturday.

The judge also compelled the unidentified customers to hand over the novel to Raincoast, which has agreed to return them signed by Rowling, along with other gifts, after the official launch.

The first five Harry Potter books have sold nearly 300 million copies worldwide.

AFP