LOS ANGELES/LONDON (Reuters) - "Harry Potter and the Cursed Child," the script for a new London play telling the eighth story in the boy wizard series, has sold more than 2 million copies in its first two days on the market in the United States, publisher Scholastic said on Wednesday.

The book - a script instead of a narrative novel like author J.K. Rowling's previous Potter books - was published at midnight on Sunday, shortly after the play's gala opening. The play is sold out through May 2017.

"Cursed Child," written by Rowling, screenwriter and playwright Jack Thorne and director John Tiffany, is set 19 years after "Harry Potter and the Deathly Hallows," the final book in the original series, released in 2007.

Scholastic, the U.S. and Canadian publisher of "Cursed Child," said the sales figures were unprecedented for a script book. Prior to its release, Barnes & Noble said "Cursed Child" was the most pre-ordered book since 2007's "Deathly Hallows."

Scholastic said it had ordered 4.5 million first printing copies of "Cursed Child" and retailers had reported "fast-paced, record-breaking pre-sales" ahead of the release date.

Full first-week U.S. sales figures of "Cursed Child" from Nielsen BookScan are not expected until next week.

U.K. publisher Little, Brown Book Group said "Cursed Child" sold 680,000 print copies in the U.K. in three days.

U.K. book industry magazine and website The Bookseller said if the sales rate continued, the script book would "be the second biggest-selling single week for one title since records began, with 'Harry Potter and the Deathly Hallows' as the first."

"Deathly Hallows" sold 1.8 million copies and 780,000 units of the adult edition in the U.K. in its launch week, it added.

Bringing back Rowling's enchanted world of witches and wizards, "Harry Potter and the Cursed Child" features Potter as a father of three and an overworked employee of the Ministry of Magic.

Kate Skipper, buying director at U.K. bookstore chain Waterstones, said "Cursed Child" is already the store's biggest-selling hardback since Dan Brown's 2009 thriller "The Lost Symbol" and that it is expected sales would exceed those of "The Lost Symbol" by the end of its first week.

"Cursed Child" is also expected to match the overall sales of Waterstones' bestselling script book ever, J.B. Priestley's "An Inspector Calls."

"There's no doubt about it, this will be our biggest book of the year," Skipper said in a statement.

(Reporting by Piya Sinha-Roy and Marie-Louise Gumuchia; Editing by Leslie Adler)