KARACHI, Pakistan — A powerful explosion at a fireworks factory in southern Pakistan on Saturday killed at least four people and injured 11 others, police and hospital officials said.

Footage shared on social media showed thick plumes of smoke rising from a collapsed building where firecrackers were being made in Hyderabad city in Sindh province. City police chief Adeel Chandio said rescuers transported the dead and injured to a hospital.

He said the cause of the blast was not immediately known.

The Sindh government said in a statement that an investigation would determine whether the factory had permission to manufacture fireworks and followed safety procedures.

Explosions at fireworks facilities are common in Pakistan. In August, five people were killed when a blast tore through a fireworks storage site in the southern port city of Karachi.