A statement from Warner Bros. Pictures said the original November release date for "Harry Potter and the Half-Blood Prince", the sixth movie adaptation of J.K. Rowling's books, had now been shifted to July 17, 2009.

Warner president Alan Horn said the decision was taken to guarantee the studio a major summer blockbuster in 2009, and was partially explained by the Hollywood writer's strike, which paralyzed the movie industry this year.

"Like every other studio, we are still feeling the repercussions of the writers' strike, which impacted the readiness of scripts for other films -- changing the competitive landscape for 2009 and offering new windows of opportunity that we wanted to take advantage of," Horn said.

"We agreed the best strategy was to move 'Half-Blood Prince' to July, where it perfectly fills the gap for a major tent pole release for mid-summer."

A "tent pole" movie is usually a big-budget, heavily promoted film relied on by a studio to turn a profit rapidly.

Horn said a summer release date would benefit box office revenues, citing the most recent Harry Potter film, the second-highest grossing film in the franchise after the first instalment.

Jeff Robinov, president of Warner Bros. Motion Picture Group, said the change would not affect production of future Harry Potter films, the two-part "Harry Potter and the Deathly Hallows," the final installment in the series.

"The good news (for fans) is that the gap will now be shortened between 'Half-Blood Prince' and the first part of 'Harry Potter and the Deathly Hallows,'" Robinov said.

The five Harry Potter films released so far have grossed more than 4.47 billion dollars worldwide since 2001, making it one of the most lucrative franchises of all time in terms of box-office.