The Senior Superintendent Police (SSP) City Adeel Chandio said the grenade attack took place in Kharadar's Chagla Street.
The injured were rushed to the hospital for medical assistance.
An investigation is underway as the Sindh Home Minister Sohail Anwar Siyal has asked for a detailed inquiry report from the deputy inspector general (DIG) South.
Earlier on Sunday, Muttahida Qaumi Movement (MQM) leader Dr Hasan Zafar Arif was found dead in a car in Karachi's Ilyas Goth area.
Dr Arif, who was also the MQM-London's deputy convener, used to teach Philosophy at the University of Karachi. (ANI)