At least 10 people were killed and at least 11 others wounded in an explosion on Saturday (September 18) at a Karachi bank branch constructed on a sewage drain, police said.
The cause of the blast, at a branch of Pakistan's largest bank, Habib Bank Limited, could be a gas leak, a senior police officer said.
A petrol station located next to the bank in the Sindh Industrial Trading Estate, and cars parked nearby, were badly damaged.
The bank's floor was ripped apart, exposing twisted iron bars.
A senior police officer told reporters it was not immediately clear how many were dead or injured in the explosion as the bank had a skeleton staff on Saturday.
Construction laws are often flouted in Pakistan.
Several sewage drains have been concreted over in Karachi to make way for parking lots.
Last month, the country's Supreme Court ordered the demolition of a multi-storey apartment building found to have been constructed on an illegal plot at Karachi's main thoroughfare.