“At least two policemen were killed in the blast in Quetta,” Liaquat Shahwani, spokesman for the Balochistan government, said in a statement on Sunday.
The injured have been moved to the city’s Civil Hospital, a senior police official said.
Shahwani said four passersby were also wounded in the blast that targeted the police mobile van at Tanzeem Square near the upscale Serena Hotel.
The bomb, which was planted on a motorcycle, went off near a van full of policemen, a local police official said, adding that the windows of nearby buildings were shattered by the explosion.
No group has yet claimed responsibility for the attack.
Security agencies have cordoned off the area and launched a manhunt to arrest the culprits, Shahwani said.
Balochistan, which shares a border with both Afghanistan and Iran, is Pakistan’s largest and most volatile province.
It faces a multifaceted threat from armed groups, including the Taliban, Sunni fighters targeting Shia Muslims, and nationalist rebels seeking independence for their province.
The violence is partly seen as a response by rebels to Beijing’s investment plans linking China’s Xinjiang province with the Gulf of Oman via Balochistan by way of a network of roads and rail tracks.
Attacks targeting law enforcement agencies and workers from other provinces, especially those working on projects initiated by China under a $62bn investment plan, are common in Balochistan.