A bomb explosion has rocked a busy street in the southwestern Pakistan city of Quetta, killing a four-year old girl and wounding 11 other people.

The bomb was attached to a motorcycle and exploded outside a commercial bank.

Four of the wounded were traffic police on duty nearby, and others were passers-by.

Mohammad Akbar Arraeen is the police chief.

"The IED (Improvised Explosive Device) was planted in the motorcycle which exploded. As a result of this explosion there has been 10, more than 10 injuries."

There was no immediate claim of responsibility.

Quetta is the capital of southwestern Baluchistan province where authorities have blamed armed tribesmen for bombings and attacks against the government.

Ethnic Baluch tribesmen are waging a low-level insurgency to press calls for greater provincial autonomy and control over natural resources in Baluchistan.