The Kill Bill star, 72, was staying in Bangkok while shooting his new movie Stretch.
Local media in Thailand initially reported that Carradine had committed suicide by hanging himself in his hotel suite, but the star's agent has told a TV station that he believes the actor died of natural causes.
Carradine's manager Chuck Binder says a producer of the Stretch movie found the actor dead when he called his room at the Park Nai Lert Hotel in Junfan Mulay, Bangkok.
But police in Thailand insist a hotel maid had found Carradine dead in a wardrobe with a rope around his neck and body on Thursday morning. A spokesman declined to give further details out of consideration for the actor's family.
Paying tribute to Carradine, Binder said: "(His death is) shocking and sad. He was full of life, always wanting to work... a great person."
He took a course in drama at San Francisco State University, before changing his name to David and launching his career on the stage.
He appeared in more than 100 films and TV dramas, working with prestigious directors including Martin Scorsese and Ingmar Bergman, but was best known for his roles as Kwai Chang Caine in the 1970s series Kung Fu and as the title character from Quentin Tarantino's martial arts films Kill Bill Vols. 1 and 2.
In 2005, he was awarded the Action On Film International Film Festival Lifetime Achievement Award in honor of his 45-year career.
Carradine was married five times -- most recently to Annie Bierman in 2004 -- and had two daughters, Calista Miranda and Kansas.
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