The explosion took place on Saturday noon in front of 'ShirShah Square' in Karachi, the capital of Sindh province in southern Pakistan on a gas pipeline passing through the area.
Twelve people were killed and 12 more injured in the blast.
Search and rescue operations are currently underway and there may be more casualties.
Four of the injured are in critical condition, according to Pakistani officials. Rescuers are on the scene to transport the injured to a hospital for treatment.
The blast severely damaged several units including a bank building and caused a fire at the scene.
Eyewitnesses say many people are buried under the rubble of the building.
Karachi police are investigating the blast.
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