The target of the attack was said to be a vehicle of the Frontier Corps (FC).
According to eye witnesses and rescue workers, the powerful blast rocked the entire Qambrani road and surrounding areas.
"We could see thick black smoke from quite a distance," Fateh Muhammad, an eye-witness told Dawn.
Police and paramilitary troops were called in the area to bring the situation under control.
"The bomb was planted on a motorcycle," Imran Qureshi, Senior Superintendent of Police(SSP) Sariab said.
The blast was followed by intense firing and panic spread in the area and, people were confined to their homes and shops.
This was not the first incident of violence on the perilous Qambrani road of the provincial capital. Militants in recent days have intensified attacks against security forces and national installations in Balochistan, plagued by an insurgency and growing sectarian killings for more than a decade.