A Toyota Prado was heading along Hansens Road about 6.15pm on Sunday when it rolled. Three men, all 19 years old, were thrown from the vehicle's back seat.
Police said the middle-seat passenger was flown to the Royal North Shore hospital. He has undergone surgery after suffering suspected spinal injuries.
The passenger who was riding behind the driver has suspected leg fractures and was flown to the John Hunter hospital while the man who was behind the passenger seat has shoulder and rib injuries.
Both he and a front seat passenger were taken to Gosford hospital. The 22-year-old in the front seat suffered neck and head injuries.
The 19-year-old driver, from Tuggerawong, was taken to Gosford hospital as a precaution and to undergo mandatory blood and urine testing.
Crash investigators and Tuggerah Lakes police are examining the circumstances of the crash, and have seized the car for mechanical examination.
Inquiries are continuing and anyone with information is urged to call Crime Stoppers on 1800 333 000.
The incident came just hours after two Hunter deaths.
Friends were unable to revive an 18-year-old bodyboarder who suffered cardiac arrest at Pinny beach on Sunday morning, while a 62-year-old cyclist died after hitting a truck on Koorang Island less than two hours earlier.