Detectives from the Met's Trident gang crime command are investigating a drive-by shooting close to Waterloo Bridge on Friday night.
The emergency services were called to Waterloo Bridge at about 8pm on Friday to reports of a shooting.
Police believe that someone on a motorcycle opened fire on a black Ford Focus travelling southbound.
The incident took place on the southbound carriageway of the northern approach to the bridge, close to Somerset House.
A 22-year-old man was taken to an east London hospital with head injuries. He has since been discharged.
Three men in their early twenties were arrested on suspicion of firearms offences.
"The surrounding area, including the South Bank, would have been busy with people enjoying their Friday night and detectives are eager to speak with anyone who witnessed the shooting, or who saw the motorcycle fleeing the area," said a Metropolitan Police spokesman.
Any witnesses or anyone with any information should call police on 101 or call Crimestoppers anonymously on 0800 555 111.
The Trident Gang Crime Command is investigating.