At least 16 people, including children, were killed Thursday when an explosion caused a building to collapse in Pakistan’s southern megacity of Karachi, officials said.

More than a dozen people were injured in the incident in the Soldier Bazaar neighbourhood of Karachi at around 4 a.m. local time, when Muslim families start preparing sahur, the pre-sunrise meal eaten during Ramadan.

"Sixteen people, including women and children, have been killed and 13 others injured," the provincial rescue agency's spokesman Hassan Khan said.

The three-story building located in the crowded neighborhood collapsed after an "unknown" explosion, he said.

"Apparently, it was a gas explosion, but the investigation will reveal the actual cause of the incident," senior city official Nasrullah Abbasi told AFP.