A 21-year-old woman was trapped under the bonnet of a car after it flipped on to its roof following an accident.
The incident happened at the junction of Madeira Drive and Duke's Mound in Brighton at about 3.30am today.
A Renault Clio being driven by a 23-year-old Crawley man was in collision with a Mini being driven by a man of 19 from Angmering.
The Renault ended up on its roof, trapping the female passenger inside.
She was cut free by firefighters and taken to the Royal Sussex County Hospital in Brighton for treatment.
The woman suffered serious injuries although they were not considered to be life-threatening.
The Renault driver was also taken to hospital with minor injuries.
The Mini driver was arrested on suspicion of causing serious injury by dangerous driving.
The Renault driver was also arrested on suspicion of being drunk in charge of a motor vehicle
Police are appealing for witnesses.
Anyone able to help is asked to call 101 or email firstname.lastname@example.org, quoting Operation Canberra.