The Easy Rider star, 73, was taken ill on Wednesday afternoon with a stomach complaint, his representative has confirmed.
His full condition was unknown as WENN went to press.
As a result of his illness, Hopper has been forced to pull out of several appearances on talk shows including Late Night With Jimmy Fallon and Today.
The actor is in the Big Apple to promote his TV show Crash, a series based on the Academy Award-winning 2004 movie.
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