Steven Spielberg (search) and Tom Cruise's (search) sci-fi thriller "War of the Worlds (search)" 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 (search) classic about invaders from outer space earned about $34.6 million worldwide when it debuted Wednesday, Paramount Pictures (search) said.

The haul marked the most 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 (search)," whose record $180.1 million in its first six days paced the industry to its best Fourth of July ever.