The officer in charge of the police station was among the wounded who were rushed to a hospital.
The police sergeant who carried out the shooting has been arrested after he surrendered to a separate police station and handed over two T-56 assault rifles and ammunition, police spokesman Nihal Thalduwa said.
The motive for the shooting was not immediately known.
A police team headed by a senior officer in the area has been deployed to probe the incident, Thalduwa said.