Director David Yates on the set of "Harry Potter and the Half-Blood Prince".[Agencies]

NEW YORK - The sixth "Harry Potter" film opens on Wednesday and is likely to be another hit for the boy wizard series, but with filming started on the finale, British director David Yates says "you haven't seen anything yet."

"Harry Potter and the Half-Blood Prince," in which romance, magic and comedy collide as teenage hormones rage at Hogwarts School of Witchcraft and Wizardry, has received rave reviews and already sold out hundreds of theaters for its opening day.

Based on author British author J.K. Rowling's seven novels, which have sold more than 400 million copies, the film franchise has so far raked $4.5 billion worldwide for Warner Bros. studio, which is owned by Time Warner Inc.

The series finale is being split into two movies for which filming began five months ago and is due to finish in about a year. Part one of "Harry Potter and the Deathly Hallows" is due out in late 2010 and part two is planned for release in 2011.

"People are being very kind about what they're seeing in 'Half-Blood Prince' and I just think you haven't seen anything yet," Yates, who directed "Harry Potter" five and six and is helming the final two, said in a recent interview.

"(Part one) is like a road movie, refugees being chased by all these people who want to kill them. It's quite intense," he said. "Then the final film is like this big opera, big epic, it's got more set pieces than any of the others."

"It's fights and dragons and battles," he said. "It's a real rollercoaster, but with a really oddly uplifting end."

Website Rottentomatoes.com, which collates movies reviews, said 96 percent of critics liked "Harry Potter and the Half-Blood Prince." Variety magazine said the movie is set to become "one of the year's two or three top-earning films."

ROWLING TO "POP IN" MORE OFTEN

The three key cast members who have played their characters throughout the series -- Daniel Radcliffe (Harry Potter), Emma Watson (Hermione Granger) and Rupert Grint (Ron Weasley) -- said they were excited about the final films.

"I feel like I'm on this totally different film," Watson, 19, told a news conference. "All of us are now finished with school and we're just totally focused on this finale."

Radcliffe said he didn't want to start contemplating the end of the film yet, which he likened to his "dream coming to an end," while Tom Felton, who plays Potter enemy Draco Malfoy, said he would "cry my eyes out" when it's finished.

Author Rowling has said she was devastated after finishing the final "Harry Potter" book, which was published in July 2007 by Scholastic Corp in the United States and Bloomsbury Publishing elsewhere in the world.

The books, which she spent 17 years working on, have made the mother-of-three one of the world's wealthiest writers.

Rowling has also remained involved throughout the making of the films, reading scripts before shooting begins and offering suggestions, Yates said.