A police official said that the SSP remained unhurt while his two guards received injuries.
Casualty staff of Jinnah Post Graduate Medical Centre (JPMC) said that two of the deceased have been identified as Atta son of Rashid, 60, a bank employee and Adeel, 30, a passerby. They said two of the injured had died on the spot while remaining succumbed to injuries during treatment.
A police official suspected that one of the unidentified persons may be a suicide bomber riding the bike.
A volunteer of Edhi Ambulance Service said that 16 injured, four of them with critical wounds were shifted to the JMPC.
Bomb disposal squad sources said that the bomb carried 4 to 5 kilogram of explosive with sharp objects and ball bearings which pierced through the APC.