Firefighters and police were responding, and the street contained at least two damaged cars.
The crash appeared to be on Broad Street, near the city landmark, police said.
CNN first learned about the crash on Twitter.
CBS reports the Seattle Fire Department said in addition to the fatalities, a 37-year-old man who managed to free himself from a car at the accident scene was taken to Harborview Medical Center in critical condition. No other details were immediately available.
The station says the copter was apparently lifting off from its rooftop Tuesday morning when it possibly hit the side of the building and went down, hitting several vehicles on Broad Street.
The copter and cars exploded in flames.
The FAA said the crash occurred at about 7:40 a.m. and local authorities said that there were three people on board.
(information provided by CNN and CBS)
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