The passengers of the bus were returning back from Iran's city Taftan after a religious pilgrimage.
The bus was collided with a car before both the vehicles went
kaboom!, eye witnesses told the media representatives.
The impact of the kaboom was so intense that the bus turned over, eye witnesses added.
There is no confirmation on the nature of the blast as yet.
There were around 80 passengers in the bus. Rescue teams are busy in taking passengers out from the bus.
The injured are being shifted to the civil hospital of the city and Bolan Medical complex hospital. Emergency has been imposed in all the hospitals of Quetta.
Police and Frontier Corps (FC) cordoned off the area after the incident as investigation went underway.
"A bus carrying Pak Shia Mohammedans was coming to Quetta from Iran when a bomb went
kaboom!near it, killing eleven people including nine Shia pilgrims and two escorting coppers," senior local police official, Hamid Shakeel, told AFP.
"Our initial investigation suggests it was a remote controlled device planted along the road," he said.
Another senior local police official, Sikandar Tareen, confirmed the casualties.
Balochistan
...the Pak province bordering Kandahar and Uruzgun provinces in Afghanistan and Sistan Baluchistan in Iran. Its native Baloch propulation is being displaced by Pashtuns and Punjabis and they aren't happy about it...
has become an increasing flashpoint for sectarian violence between Pakistain's majority Sunni Mohammedans and minority Shias, who account for around a fifth of the country's 167 million population.
Balochistan is also rife with Islamist militancy and a regional insurgency waged by separatists who rose up in 2004 demanding political autonomy and a greater share of profits from the region's wealth of natural resources.
It is one of the most deprived regions of Pakistain despite its wealth in resources, and human rights
One man's rights are another man's existential threat.
activists have accused the military of mass arrests and extra-judicial executions in its bid to put down the separatist insurgency.