"There were no safety measures taken in the building design. There was no emergency exit. All the people got trapped," said senior police official Amjad Farooqi.
The factory's managers have fled and are being sought by police, said Sheikh, the senior government official in Karachi. Authorities have placed the name of the factory's owner on a list of people who are not allowed to leave the country, said Sheikh.
A fire also swept through a four-story shoe factory in Lahore on Tuesday night, killing 25 people, some from burns and some from suffocation, said senior police officer Multan Khan.
The factory was illegally set up in a residential part of the city.
It broke out when people in the building were trying to start their generator after the electricity went out.