Police opened fire at a motor car which was travelling disobeying the police orders to stop at Egoda-Uyana, Moratuwa, police said.
They said four people in the vehicle were arrested while three of them, who were injured in the shooting, were hospitalised.
Two of the injured are undergoing treatment at the Panadura Hospital while the other was transferred to the Colombo National Hospital.
Police said the injured aged between 18 and 22 were residents of Panadura and Battaramulla.
According to the initial investigations, one of the injured had been in remanded custody in 2018 over possession of heroin and another injured had also been in remand custody in 2017 and 2019 over heroin case and drug trafficking.
Investigations are underway to determine whether they were transporting narcotics at the time of the incident.