TMZ reported "The French Connection" and "Superman" star was airlifted to a trauma hospital after the incident Friday afternoon.
His representative insisted the two-time Oscar-winning actor is "fine" and only "suffered bumps and bruises after a woman bumped him from behind in her vehicle." He has since been released from the hospital.
The Florida Highway Patrol told the celebrity news Web site the collision in the Florida Keys was under investigation.
Hackman won the best actor Oscar in 1971 for "The French Connection" and the supporting actor Oscar in 1992 for "Unforgiven."