"It was a time device and, judging by the impact of the blast, it appears to be very heavy explosive," Ali said.
A regional police chief told the AFP news agency that the bomb had been detonated by remote control.
Police cordoned off the scene and bomb disposal squad officers collected evidence and fragments of the bomb. "It was a locally made high-intensity device," one officer told AFP.
The blast came nearly two weeks after a suicide bomber blew himself up in a packed courtroom in the southwestern city of Quetta, killing at least 15 people including the city's senior civil judge.
Pakistan has seen a series of bomb attacks since an airstrike on an alleged al-Qaeda and Taliban compound near the Afghanistan border in January.
Intelligence officials have linked the series of attacks, that have killed nearly 50 people this year, to Islamic groups seeking to destabilise the government of Pervez Musharraf, the president.