According to police, the blast took place near Murghi Khana area at Quaidabad when a police van (Special Security Unit bus) was attacked. The policemen were going for the security of Bilawal House.
The victims were identified as Gulzar and Chandar, the police said.
SSP Rao Anwar told media that the explosive material was planted in a motorcycle. He also told that two of the policemen were in a critical condition.
The injured people were shifted to Jinnah Postgraduate Medical Centre for immediate treatment.
The police have started investigation and search operation in the surrounding areas of Quaidabad.