In this promotional shot, actor Heath Ledger is pictured seated as The Joker while Christian Bale as Batman stands behind him in a scene from The Dark Knight, which came out July 18. (Stephen Vaughan/Warner Bros./AP)

The latest Batman movie, The Dark Knight, has soared to new heights, raking in more than $500 million U.S. at the North American box office, only the second movie ever to do so in that country.

The film, starring Christian Bale in the title role and the late Heath Ledger as The Joker, reached that milestone in just six weeks — half the time it took 1997's Titanic to hit that benchmark.

Titanic, directed by Canada's James Cameron, still holds the top spot for overall North American take at $600.8 million U.S.

The Dark Knight, released on July 18, is not expected to challenge that position but could reach $550 million U.S., according to officials at Hollywood studio Warner Bros.

"It just keeps holding better than expected," said Dan Fellman, head of distribution at the studio.

Directed by Christopher Nolan, The Dark Knight has millionaire Bruce Wayne battling an out-of-control Joker, whose aim is to cause anarchy in Gotham.

Some critics have hailed Ledger's performance as Oscar-worthy, including co-star Michael Caine.

The Australian actor died of an accidental overdose of prescription drugs in January.

With files from the Associated Press