The 73-year-old actor was seen wearing an oxygen mask when he was rushed by ambulance to the emergency room of a Manhattan hospital, sources told Entertainment Tonight.
Hopper was at NBC headquarters at 30 Rockefeller Plaza earlier Wednesday, as he was scheduled to make a number of NBC appearances, but left after feeling ill.
Hopper, who was in town to promote his TV series "Crash," was hospitalized after developing flulike symptoms, said his publicist, Sheila Feren.
Hopper was forced to cancel a number of interviews and TV appearances, including "Today" and "Late Night With Jimmy Fallon," where he was replaced by Jack McBrayer of "30 Rock."
The twice-Oscar nominated actor has gotten nods for co-writing "Easy Rider" in 1969 and for his performance in "Hoosiers" in 1986. Hopper's management would not confirm or deny the Entertainment Tonight report but said a statement would soon be issued.