Kandahar police spokesman Ghorzang Afridi said the assault killed six people and wounded four others.
"All the victims were local policemen," Afridi told AFP.
"The explosion was very loud and you could hear the sound of the blast miles away from the headquarters," a local police officer told AFP on the condition of anonymity.
He put the death toll at eight with nine others wounded.
"The eight policemen who were killed have been removed or pulled out from under the rubble, and there were other policemen who went missing following the attack," the officer said.
The Taliban have stepped up attacks on security installations as they seek to demoralise police and troops, and steal equipment to fuel the 16-year insurgency.
The militants have acquired "dozens" of armoured Humvees and pickup trucks in recent years, officials have said.
Some of those vehicles have been used in suicide attacks on police and military bases with devastating effect.
Afghan forces, already beset by desertions and corruption, have seen casualties soar to what a US watchdog has described as "shockingly high" levels since NATO forces officially ended their combat mission in 2014 and began a training and support role.
Morale has been further eroded by long-running fears that the militants have insider help -- everything from infiltrators in the ranks to corrupt Afghan forces selling equipment to the Taliban.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)