At least 18 people were killed and 51 injured when the roof of a factory collapsed near the eastern Pakistani city of Lahore, officials said, with around a hundred more still trapped.
The incident on Wednesday (local time) comes less than two weeks after a powerful 7.5-magnitude earthquake ripped across Afghanistan and Pakistan, killing nearly 390 people, levelling thousands of homes, and causing structural damage to major buildings.
"We have recovered 18 dead bodies and more than 70 people alive, 51 of them are injured and have been taken to hospitals," said Mohammad Usman, the top administration official in Lahore who was coordinating the response to the disaster in the city, the capital of Punjab province.
"Rescue work is ongoing," he said as teams of rescuers, police and soldiers worked through the night under lights searching for survivors beneath the rubble of the four-storey factory.
The army said it was deploying specialist search teams and engineers to help the rescue effort.
The collapse occurred at a Rajput Polyester polythene bag factory in the Sundar industrial estate around 45 kilometres southwest of the city centre.
Jam Sajjad Hussain, a spokesman for the rescue services, said 100 people were still trapped several hours after the roof collapsed, while ambulances were taking the injured to hospital.
"All our rescue workers are on site but it is such a big incident that we have called rescue workers from other nearby districts," he added.
Punjab chief minister Shahbaz Sharif said it was possible the building had been damaged after the October 26 earthquake.
"I have heard about the earthquake affecting the building, but according to labourers the owner continued to build an extension," he told reporters.
Three cranes, a bulldozer and more than 40 emergency rescue vehicles were working at the site, a rescue official said.
But provincial spokesman Zaeem Qadri told reporters that progress was slow because the factory was at the end of a narrow lane making it difficult for excavators to reach the site.
He added that an emergency has been declared at all local hospitals.
Chief doctor Zia Ullah of Jinnah Hospital where some injured have been taken said most of the victims were young workers, with many suffering head injuries and fractured limbs.