Police official Haroon Khan said that the nature of the blast is yet to be determined.
The blasts took place when the Police Public School, run by police welfare foundation, was in session. The foundation helps in raising money for the families of police officers.
In another separate incident, suspected Taliban militants in the northwest detonated two bombs. A pair of oil tankers, including a vital supply route used by NATO and US forces in Afghanistan were destroyed in the attack.
Local official Iqbal Khan said that there has been no casualty in the attack.
Pakistan has been plagued by a series of suicide attacks in the past two days.