LOS ANGELES - Steven Spielberg and Tom Cruise's sci-fi thriller "War of the Worlds" raked in about $21.3 million at the domestic box office on its opening day, according to studio estimates released Thursday.

Spielberg's update of the H.G. Wells' classic about invaders from outer space earned about $34.6 million worldwide when it debuted Wednesday, Paramount Pictures said.

The haul marked the must successful first day for a Cruise movie, the studio said.

Even with a big Fourth of July weekend expected from the film, it may not be enough to lift the industry out of its longest modern box-office slump. Domestic movie revenues have declined for 18 straight weekends compared to 2004.

The film opens over the same long weekend as last year's "Spider-Man 2," whose record $180.1 million in its first six days paced the industry to its best Fourth of July ever.