At least 13 people were killed and over 200 injured on Friday afternoon in a suspected suicide bomb attack on a mosque packed with Shia worshippers in Pakistan's port city of Karachi.

The blast occurred in the mosque situation inside a government-run religious school at around 1350 IST during the Friday prayers, reports reaching Islamabad said.

The blast virtually ripped open the mosque's high ceiling and created mayhem. Television channels showed bits of flesh and pools of blood all around as rescuers shifted the wounded in ambulances to hospitals.

No one has claimed responsibility for the attack.

While 12 dead were brought to Karachi Civil Hospital, another body was taken to the Jinnah Hospital. About 50 injured people were in hospitals while others were discharged after treatment of minor injuries.

Soon after the blast, Shia mourners attacked police vehicles with stones and attempted to set them on fire.

Another bomb exploded in the premises of the high court building in Quetta, the provincial headquarters of Pakistan's southwestern Baluchistan, injuring a policeman and a bystander.

The bomb, believed to have been placed at a cycle-stand, went off at around 1100 IST, witnesses said.