The gunmen fired at people at a shop in Sirki Road in Quetta, the capital of Balochistan province, on Sunday afternoon.
Five persons were killed instantly while a policeman succumbed to his injuries while being taken to hospital, witnesses and officials said.
Another policeman was among the injured, officials said.
Footage on television showed bodies and the injured being taken to the Civil Hospital in Quetta by volunteers and rescue service officials.
No group claimed responsibility for the attack, which was carried out shortly before the arrival of Prime Minister Gilani.
The premier is scheduled to chair a high-level meeting to review the law and order situation in Balochistan and sensitive issues like the case of "missing persons" or those detained without charge by security and intelligence agencies.
Civil society groups have alleged that hundreds of people have been detained by security agencies for alleged links to insurgent groups.
The bodies of over 200 "missing persons" have been found across Balochistan in recent months.
Islamabad: Unidentified gunmen shot and killed six persons, including a policeman, and injured several others in Quetta city of southwest Pakistan on Sunday shortly before the arrival of Prime Minister Yousuf Raza Gilani.
First Published: Sunday, June 03, 2012, 15:29