Police on Sunday launched an investigation into the deadly sewerage line blast in Karachi's Shershah area as the incident's death toll rose to 17 with the discovery of two more bodies.

A building housing a private bank collapsed, while a nearby petrol pump and some vehicles were damaged in the Saturday afternoon explosion caused by accumulation of gases in the drain underneath.

Site-B police have registered the FIR of the incident against the "persons responsible for the construction of the building and its owner" under various charges including manslaughter, said an area police officer.

The case has been registered on behalf of the state through Site-B Station House Officer Zawar Husain.

Police officer Asghar told Dawn.com that two more bodies had been recovered from the debris at around 1:30am on Sunday, raising the death toll to 17.

According to the FIR, the blast took place at around 1:45pm on Saturday near a private bank adjacent to a petrol station located on Estate Avenue Road, SITE at Shershah Chowk.

Contingents of police rushed to the spot and later called bomb disposal and crime scene units, and rescue organisations to help in rescue work.

A team of the BDS led by inspector Mohammed Amir also arrived at the spot and after examining the place submitted its report to the complainant, SHO Zawar Husain.

“The BDS team in their report stated that the blast occurred due to the release of gases from the sewerage line beneath the building housing the bank and another office,” the FIR says.

“This report and an examination of the site showed that the bank and the other office were constructed on the sewerage line illegally and continuous leaking of gases from the nulla (drain) caused this incident.”

The building was constructed by encroaching upon the land of the drain. The owner of the building and those who constructed it will be charged under Sections 322 (Punishment for qatl-bis-sabab), 337-H (Punishment for hurt by rash or negligent act), 337-I [Punishment for causing hurt by mistake (khata)], 427 (Mischief causing damage) and 34 (common intention) of the Pakistan Penal Code.

Evidence to be sent for forensic analysis

DIG South Sharjeel Kharal confirmed that the death toll had risen to 17, adding that an investigation into the incident had been launched.

"Investigators have collected debris, an electric wire piece, sewage water, wood pieces and CCTV DVR as evidence and further footage is being collected," he said. "The evidence will be sent to a laboratory for forensic analysis to ascertain the reason for the explosion."

He revealed that seven people, including five bank staffers, had died inside the bank, while 10 people died outside the bank.

According to DIG Kharal, the father of PTI MNA Alamgir Khan had his car showroom adjacent to the bank; he was present there when the blast occurred and lost his life.

To a question about a second explosion, the officer said a short circuit failure had occurred after the explosion, without causing any injury to anyone. Police called K-Electric officials who disconnected electricity in the area to remove the debris.