The accident took place in a mountainous area. The bus was enroute to Quetta and had at least 50 passengers on board.
Locals began rescue efforts whereas rescue teams set off from Islamabad and Rawalpindi, too.
The injured were being shifted to the District Headquarters (DHQ) hospital. The death toll is expected to rise.
Earlier, two people were killed and three others were wounded in Ziarat on Sunday, when a van of picnickers on the way to Baba Karwari plunged into a deep ravine.
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