At least one was killed and 11 others including three cops were injured when a roadside planted bomb hit Pakistan's southwest city of Quetta on Monday, sources in Quetta told Xinhua.

According to the sources and local media reports, the blast took place at about noon time when a bomb fixed in a motorbike parked by the roadside went off on the Double Road in the city.

The target of the bomb was a police vehicle, said local media, adding that the bomb was detonated when the police vehicle was passing by.

At least three policemen were injured in the explosion. Several vehicles and nearby building were also damaged in the blast.

Police and Frontier Corps, a paramilitary force in Pakistan, cordoned off the area after the blast.

Bomb disposal squad said an estimated 5kg of explosives were used in the bomb.

All the injured people have been shifted to civil hospital in the city. Hospital sources said that some of the wounded were in critical condition.

No group has claimed responsibility for the attack yet.