According to the motorway police spokesperson, the incident occurred when the bus was en route to Raiwind from Swat and its brakes failed.
The bus overturned after a head-on collision with a truck.
The injured were shifted to the Fauji Foundation Hospital in Kallar Kahar where three of them were said to be in a critical condition.
The motorway police had arrived at the scene after they were notified and had started the rescue operation.
Earlier, 35 people including 32 schoolchildren were killed when an overloaded and unfit bus overturned on the accident-prone Kallar Kahar area.
(Read: Kallar Kahar accident: Inquiry teams meet survivors, record statements)
The bus was carrying 101 students and five staff members, who were on their way back from a school trip to Kallar Kahar and Khewra Salt Mines, widely-known as tourist destinations.
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