Around 12 people were killed and 11 others injured in Pakistan's financial capital of Karachi on Saturday when a massive blast, apparently triggered by a gas explosion in a sewage canal, ripped through the building of a private bank situated on it, police said.

Most of the casualties are reportedly customers and staff present inside the bank which was built on top of a covered sewage channel in Karachi's Shershah area and collapsed following the explosion, the Express Tribune newspaper reported.

Officials said that the cause of the explosion is being probed as it cannot be ascertained whether it was a gas pipeline or a build-up of methane that took place inside the sewage system which led to the explosion.

Sabir Memon, a doctor at the Trauma Center in Karachi, said at least three people among those injured in Saturday’s incident were in a critical condition and several had been sent to the intensive care unit.

Police spokesman Sohail Jokhio said the explosion was likely caused by accumulated gas in the sewer beneath a bank building in the city’s Shershah neighbourhood.

“We have no idea whether it was a gas blast. Our first priority is the rescue operation and then we can determine the cause of the explosion,” said Sharjeel Kharal, Police Deputy Inspector General (DIG) for the South region.

Footage of the blast showed a damaged building and debris on the ground along with damaged vehicles as rescue workers were trying to retrieve the injured.

According to a report in Geo TV, eyewitnesses claim that there are many people who are buried underneath the debris of the building.

Excavators have been called to the site to remove the debris and rescue any persons trapped there.

A bomb disposal unit (BDU) has also arrived at the location which has been cordoned off, the Geo TV report said.

Sindh Chief Minister Murad Ali Shah has ordered a detailed inquiry into the incident

The Geo TV report said that a second blast took place during the rescue and search operation when a few electric wires, which were being taken down, collided with the gas line but no loss of life was reported.

The explosion occurred a day before Pakistan was hosting the 17th extraordinary meeting of the OIC foreign minister in Islamabad to tackle the situation in Afghanistan.

Image courtesy: Reuters