The explosion took place in an area that is densely populated and several casualties are feared.
The rescue teams are facing difficulty in carrying out rescue and relief operations due to the narrow streets as the mosque is situated near the Qissa Khwani Bazaar area.
According to Rescue 1122, the injured have been moved to the Lady Reading Hospital.
Rescue 1122 officials told currently 15 ambulances were on the site.
Officials have yet to confirm the nature of the explosion.