Buena Vista's National Treasure: Book Of Secrets proved too strong for the competition in a crowded weekend and launched at number one withan estimated $45.5m.

Nicolas Cage reprises his role as a treasure hunter who this time investigates the truth behind President Abraham Lincoln's assassination. Helen Mirren, Jon Voight and Diane Kruger round out the cast. By way of comparison National Treasure opened on $35.1m on November 19 2004 and went on to gross $173m.

The sequel inspired a second consecutive buoyant weekend at the box office as the top 12 films combined for $153.5m and finished 41% ahead of the same weekend last year.

Much of the solid weekend business was down to strong support from the second and third placed films. Warner Bros' sci-fi horror hit I Am Legend, a champion last weekend following the record November launch, soared past $100m as $34.2m raised the tally to $137.5m. Fox's children's tale Alvin And The Chipmunks fell one place to third on $29m for $84.9m after two weekends.

Universal's true life romp Charlie Wilson's War launched in fourth place on $9.6m and stars Tom Hanks as the US Senator who persuaded Congress to fund the Afghan resistance against occupying Soviet forces. Julia Roberts and Philip Seymour Hoffman also star and Mike Nichols directed.

Three other new releases broke into the top 10. Tim Burton's adaptation of the Stephen Sondheim stage musical Sweeney Todd, released in North America through Paramount and starring Johnny Depp, Helena Bonham Carter and Alan Rickman, launched in fifth place on $9.4m.

Warner Bros' romantic comedy P.S. I Love You with Hilary Swank and Gerard Butler debuted in sixth place on a lacklustre $6.5m.

But the biggest surprise was the soft performance of Sony's comedy Walk Hard: The Dewey Co story. Produced by the newly anointed golden boy of US comedy Judd Apatow, the tale of a fictitious musician played by John C Reilly managed eighth place on $4.1m.

New Line's The Golden Compass continued its miserable domestic run and fell to ninth place in its third weekend as $3.9m raised the tally to a tarnished $48.4m. Buena Vista's family film Enchanted is on the cusp of $100m after five weekends and ranks seventh on $98.4m, while Fox Searchlight's comedy Juno ranks 10th on $6.4m after three.

The Weinstein Company's drama The Great Debaters directed by and starring Denzel Washington opens through MGM on December 25, as does Fox's action horror sequel Aliens Vs Predator: Requiem, Sony's children's tale The Water Horse: Legend Of The Deep, and Warner Bros' buddie movie The Bucket List starring Jack Nicholson and Morgan Freeman.

Estimated Top 10 North America Dec 21-23, 2007

Film (Dist)/Int'l dist/Est wkd gross/Est total to date

1 (-) National Treasure: Book Of Secrets (Buena Vista) WDSMPI $45.5m -

2 (1) I Am Legend (Warner Bros) WBPI $34.2m $137.5m

3 (2) Alvin And The Chipmunks (Fox) Fox Int'l $29m $84.9m

4 (-) Charlie Wilson's War (Universal) UPI $9.6m

5 (-) Sweeney Todd (DreamWorks-Paramount) WBPI $9.4m -

6 (-) P.S. I Love You (Warner Bros) Summit Entertainment $6.5m -

7 (4) Enchanted (Buena Vista) WDSMPI $4.2m $98.4m

8 (-) Walk Hard: The Dewey Cox Story (Sony) SPRI $4.1m -

9 (3) The Golden Compass (New Line) NLI $3.9m $48.4m

10 (11) Juno (Fox Searchlight) Fox Int'l $3.4m $6.4m