The crash happened at about 3:20 a.m. near where Richardson Avenue becomes Lombard Street.
According to an initial report, a car went out of control at the curve and overturned, striking another car traveling in the opposite direction.
All four occupants of the car that flipped over were hospitalized.
One, a 17-year-old girl, had injuries that were considered life-threatening, police said.
The driver of the other vehicle was not injured.
Police are investigating whether the driver of the car that crashed was intoxicated.