Bruce Willis plays a policeman on the verge of retirement

The film, based on comic book stories by Frank Miller, beat Queen Latifah's comedy Beauty Shop into second position with Bernie Mac's Guess Who in third.

But ticket sales have shown the sixth straight weekly downturn in a row.

The latest figures are down 14% on the same weekend in 2004, reversing an initial trend at the beginning of 2005 that registered a 10% surge.

TOP FIVE NORTH AMERICAN FILMS 1. Sin City - $28.1m 2. Beauty Shop - $13.5m 3. Guess Who - �13m 4. Robots - $10m (above) 5. Miss Congeniality 2 - $8.4m Source: Exhibitor Relations, Friday-Sunday

Sin City, which was co-directed by creator Frank Miller, also stars Mickey Rourke, Lord of the Rings actor Elijah Wood and Oscar nominee Clive Owen.

In the collection of interweaving stories in a troubled metropolis, Willis plays Hartigan, a policeman accused of a crime he claims he did not commit.

Beauty Shop sees Queen Latifah reprise the role she played in Barbershop 2, which proved a hit with female audiences.

Horror sequel The Ring 2, which entered the chart at number one a fortnight ago, dropped to number seven this week after a 57% slump in sales.

The Upside of Anger, starring Kevin Costner, moved into the top 10 after its limited release was expanded.