A massive fire broke out at a chemical factory in Pakistan's southern port city of Karachi on Friday, killing at least 10 workers and injuring several others, police and a government spokesman said.

It was not immediately clear what caused the blaze in the congested Mehran Town neighborhood. TV footage showed firefighters dousing the flames, as ambulances continued transporting victims to a government hospital.

Murtaza Wahab, a spokesman for the provincial government, told reporters that the firefighters had almost extinguished the fire. He said officers had been asked to investigate what caused the fire. He said officers will also check whether the owner had installed fire extinguishing equipment.

Karachi is the capital of Sindh province, where many people have set up factories in residential areas in violation of building codes.