TMZ said Hart was riding as a passenger when his Plymouth Barracuda veered off the road, crashed through a guardrail and went down an embankment on Mulholland Highway at about 1 a.m. PST.
He and his driver reportedly suffered “major back injuries,” but a woman in the car was not seriously hurt.
Photos of the vehicle show the roof was crushed.
UsMagazine.com said it obtained a police report that said Hart “left the scene to his nearby residence to get medical attention.”
TMZ said the star was treated at a nearby hospital later in the day.
His current condition and whereabouts are not clear.
Hart, 40, is known for his stand-up comedy and performances in the films Ride Along, Central Intelligence, Jumanji: Welcome to the Jungle and Grudge Match.