Five landmines blew up on Thursday as the police officers were taking part in target practice on a firing range at the facility in Quetta, the capital of troubled Baluchistan province.
No one claimed responsibility for the explosions, but Baluchistan has been gripped for the past two years by an insurgency blamed on anti-government tribesmen.
"Six policemen were killed in blasts which were caused by landmines planted near a firing range on the outskirts of Quetta," Baluchistan police chief Chaudhry Mohammad Yaqub told AFP.
The bodies of the six were taken to a hospital in Quetta along with 28 wounded, seven of them in critical condition, doctor Fazalur Rehman said.
Two suspects have been detained in connection with the blasts, Yaqub said. Police were investigating their links with an Afghan family who lived near the site and were killed in an explosion at their home last month.
A wounded policeman, Shams-ud Din, told AFP at the hospital that some of the officers were shooting at targets and others were approaching the range when he heard a series of explosions.
Relatives gather to see the bodies
of officers killed in Quetta
"As we were busy firing, suddenly there were huge blasts nearby, and I heard people crying in pain amid clouds of smoke and dust," Din said.
Tribal rebels have been waging a revolt for the past two years to press demands for more political rights and a greater share of profits from natural resources in Baluchistan, which borders Iran and Afghanistan.
They have been blamed for attacks on police and soldiers in the province, as well as bombing of gas fields, electricity pylons, railways and other government-run facilities.
More than 150 people have died in the violence since the beginning of the year, according to official Pakistani sources.
Three landmine explosions killed three people and wounded four on Sunday in the region. In March, a vehicle travelling to a wedding hit an anti-tank mine in Baluchistan, killing 28 people, mostly women and children.
Pakistan last month outlawed a shadowy ethnic group called the Baluchistan Liberation Army and branded it a terrorist organisation.