The incident occurred yesterday in Sundar Industrial Estate area where the expansion work of the factory was going on at the four-storey building when it caved in, reports said.
"So far 18 people have been killed. Another 96 injured were recovered and shifted to hospitals," Rescue official Jam Sajjad said, adding that 99 people have been rescued so far.
The search and rescue operation went on throughout the night as there are reports of people trapped inside the rubble, he said.
Relatives expressed anger as more than 17 hours have passed since the mishap and the rescue work was still far from over. TV footage showed hapless relatives crying for support.
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Factory owner Rana Ashraf was also killed in the incident, Geo TV reported.
Known as Rajpoot Industry, the facility was used to manufacture polythene bags and part of the building was under construction with dozens of workers employed.
Punjab Chief Minister Shahbaz Sharif visited the place to monitor the rescue operation. He ordered probe into the collapse and promised to take action if human element including negligence was involved in the accident.
Army was also called in during the night as officials scrambled to clear the site. The army said specialists were deployed at the spot to help the rescue effort.
Soldiers and rescuers were busy lifting the debris of the collapsed-structure, less than two weeks after a 7.5-magnitude earthquake jolted the nation, killing nearly 400 people across Pakistan and Afghanistan.