The site, www.pottermore.com, was launched a month ahead of the release of the eighth and final Potter movie on July 15.

Some Potter fan sites, which have been instrumental in generating a large and loyal fan base for the movies and seven-book series on which they are based, were given a sneak preview of the mysterious new website.

"It is, in a word, breathtaking," wrote Leaky Cauldron, one of the leading Potter sites. "That is all we are permitted to say at the moment."

Rowling and Potter studio Warner Bros. have never shied away from building up the hype ahead of key releases in the series.

The Harry Potter novels have sold more than 400 million copies worldwide, while the seven movies released so far have grossed some $6.4 billion in ticket sales. Rowling has been billed the "world's first billionaire author."

A spokeswoman for Rowling confirmed that the site was genuine.

"We can confirm that Pottermore is indeed the name of J.K. Rowling's new project. She will be announcing it soon," she said. "It is not a new book, but we won't say more than that!"