The accident occurred when a speeding bus collided with a trailer in Mianwali district, police said.
According to Pakistani media, the traveller bus was going to Islamabad from Karachi after the driver lost control over the steering due to over-speeding.
The injured people, including women and children, were shifted to a nearby hospital, where several of them are said to be in critical condition.
Pakistan has a terrible record of lethal traffic accidents due to pitiable roads, severely upheld automobiles and irresponsible driving. Smashes slaying loads of people are not rare.