Only James Cameron's epic Titanic and the much-anticipated Star Wars prequel The Phantom Menace managed to sustain such audience interest during their first four weeks in the US and Canada.

The film, a ghostly thriller starring Willis as a therapist treating a child who talks to the dead, has taken more than $139m since it opened. It is expected to gross over $225m during its run.

It also stars Australian actress Toni Collette and British star Olivia Williams.

Saving Private Ryan battled it out for four weeks

The success of The Sixth Sense can partly be linked to the date of its release. The movie did not have to battle for audiences with the likes of Notting Hill or Wild Wild West.

The late summer opening also meant the movie was not eclipsed by the media hype surrounding the release of Star Wars: Episode 1 - The Phantom Menace.

"Typically summer blockbusters don't come out in August," says industry watcher Paul Dergarabedian. "So the timing for Sixth Sense was perfect."

As September approaches the Hollywood studios are keen to empty their vaults, releasing smaller or specialised films which promise only modest box office returns.

This lack of competition had allowed The Sixth Sense to become the first film since Saving Private Ryan to top the box office chart for four consecutive weeks.

In the past seven days The Sixth Sense has made almost twice as much money as its nearest rival, 13th Warrior, starring Antonio Banderas.

The Willis film did face a stiff battle during its opening weekend. Low-budget horror movie The Blair Witch Project almost ousted the blockbuster from the top slot - taking $24.5m to Sixth Sense's $25.8m.

The Blair Witch Project: Low-budget, big box office.

The mock documentary, which follows three students on the trail of the mysterious Blair Witch, has since slid down the box office chart. It tied for eighth place, making $4.1m in the past week.

The film, which is said to have cost around $40,000 to make, has already made more than $120m. It had its UK premiere at the Edinburgh Film Festival earlier this month.

Hollywood pundits expect the reign of The Sixth Sense to continue over the forthcoming Labor Day holiday weekend and even beyond.

Next week's debut of Chill Factor, starring Cuba Gooding Jr, and the 17 September release of the comedy Blue Streak are thought to be the only movies likely to challenge Willis' dominance.

Blue Streak stars comedian Martin Lawrence, who was rushed to hospital last week after collapsing while jogging in heavy clothing during hot weather. He is recovering after sinking into a three-day coma.