The collapse in the New Karachi Industrial area was triggered by an explosion in the factory's ammonia gas tank which stirred a gas leakage, causing the roof of the factory to cave in suddenly.
Rescue and relief officials were dispatched to the spot.
Six persons were crushed to death while four others sustained severe injuries in the incident. All the injured were rushed to a nearby hospital where their condition was not immediately known, according to rescue officials.
He said that the rescue workers and firemen were trying to clear the thoroughly damaged building in a bid to find out if there were any survivors.
In the wake of the incident, factory owner Muhammad Iqbal suffered a cardiac arrest and was admitted to a hospital.
Enforcement of labour and safety requirements and laws in factories in industrial areas are often bypassed which leads to poor and unsafe working environment for workers and labourers.