LOS ANGELES, April 13 (Xinhua) -- Two new movies grabbed the number one and two spots at box office in North America this weekend, as Hollywood continued to see a downward trend in ticket sales, preliminary figures released Sunday showed.

    "Prom Night," a high school horror movie released by Sony's Screen Gems, topped the box office with 22.7 million U.S. dollars, while Fox Searchlight's cop thriller "Street Kings" was No. 2 with 12 million dollars over the three-day period, according to a Los Angeles-based box office tracking firm Media By Numbers.

    Sony's gambling drama "21," which tells the story of a team of college students using card counting schemes to beat Las Vegas casinos in blackjack games, slipped to No. 3 with 11 million dollars after being No. 1 for two weekends. The film has grossed 62.3 million dollars in three weeks since its release.

    "Nim's Island," the 20th Century Fox family adventure film starring Jodie Foster, dropped two spots to No. 4, followed by Universal's football drama "Leatherheads."

    The dozen top-grossing films took 82.6 million dollars this weekend, about 16 percent less than what the top 12 movies earned in the same period last year, according to Media By Numbers.

    "This malaise has begun to sting an industry in a desperate need of a string of solid hits," said analysts at the box office tracking firm.