The injured had come to the police headquarters in Khawaja Ajmer Nagri to submit applications at the recruitment office and were waiting for the main gate to open and go inside.
Police said some persons on a motorcycle lobbed a RGD-1 grenade at them and fled away.
Emergency and rescue teams reached the spot and shifted the injured to Abbasi Shaheed hospital.
In an unrelated incident, two people were injured in firing in Karachi's Jahangir Road area.
Enraged protestors resorted to aerial firing and stone pelting, disrupting vehicular traffic in the area after the incident.
