It's the eighth story in the famous boy wizard series, but instead of a narrative novel like J.K. Rowling's previous Potter books, it's the script for the play that opened in London on Saturday. The screenplay was published at the stroke of midnight, just after the play's gala evening.

In the US and Canada, the book sold more than two million copies in the first two days, an "unprecedented" result for a script, according to publisher Scholastic.

It has also sold more than 680,000 copies in Britain since being published on Sunday.

"There's no doubt about it; this will be our biggest book of the year," Kate Skipper, buying director at UK bookstore chain Waterstones said in a statement.

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," said UK book industry magazine "The Bookseller."

Harry Potter play sold out through May

Written by Rowling, playwright Jack Thorne and director John Tiffany, the two-part play is set 19 years after "Harry Potter and the Deathly Hallows," the final novel in the original series, released in 2007.

The play is sold out through May 2017, but 250,000 additional tickets of the Harry Potter play are due to go on sale on Thursday.

Still far behind the success of the final novel

Despite its broken records this week, the "Cursed Child" screenplay can't keep up with the novel that preceded it.

The seventh book in the Harry Potter series was successful beyond compare: Within 24 hours of being released in 2007, "The Deathly Hallows" sold 8.3 million copies in the US and 2.65 million copies in Britain, according to the publishers for those markets, Scholastic and Bloomsbury, respectively.

Globally, the seven Harry Potter novels have sold more than 450 million copies since the first book hit the shelves in 1997. The wizard's adventures have been translated into 79 languages and adapted into eight films.

eg/kbm (Reuters, AFP)