Raunchy comedy sequel The Hangover Part II got off to a roaring start at the North American box office taking in about $31.7 million on its opening day, according to estimates by movie studio Warner Bros (TWX.N) on Friday.

The strong early start on Thursday put the movie on track to gross about $110-$125 million domestically for its five day run over the U.S. Memorial Day long weekend, Hollywood box-office watchers said.

That's despite lukewarm reviews for the sequel, which reunites actors Bradley Cooper, Ed Helms, Zach Galifianakis and Justin Bartha in another mayhem-filled bachelor party.

Critics say Hangover Part II has a plot almost identical to that of the 2009 original, but switches the action from Las Vegas to Bangkok. The Hangover grossed $468 million worldwide, making it the most successful R-rated comedy of all time.

With DreamWorks (DWA.O) family animated movie Kung Fu Panda 2, distributed by Paramount Pictures (VIAb.N) also opening, the long weekend is looking strong for Hollywood studios at the traditional start of the summer movie season.

Walt Disney Co's (DIS.N) Pirates of the Caribbean; On Stranger Tides goes into its second week after a $90.1 North American box office haul last weekend.

It's a great combination of films, said Paul Dergarabedian, box office analyst with Hollywood.com.

This is going to be one of the strongest Memorial Day weekends at the box office, with an expected gross over the four days of about $200 million, he said.

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