Senior police officials said that the four policemen were killed when unknown men on motorcycles opened fire on them outside a tea stall in Latifabad area.
"The police mobile was on duty and belonged to the A section station of Latifabad," DSP Naeem Khuro said.
He said the dead included three constables and the driver.
"It was a targeted killing," he said.
In another incident, unknown assailants opened fire on a police mobile of Sakhi Pir station injuring two policemen.
Privately, police officials say these killings are being carried out by Taliban militants in retaliation to operations by the police and rangers in many parts of Karachi and Sindh province in which several militants of TTP or other outfits have been either killed or arrested.
Two days back police claimed to have killed two activists of the TTP on the outskirts of Karachi claiming they had escaped from prison.