AFP/Reuters/Lahore

At least 18 people were killed and 40 injured when the roof of factory collapsed near the eastern Pakistani city of Lahore Wednesday, officials said, with around a hundred more still trapped.

The incident 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.

"The rescue workers have so far retrieved 16 dead bodies while at least 40 injured 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.

The toll was confirmed by Haider Ashraf, a senior local police official.

The collapse took place at a four-storey Rajput Polyester factory, which manufactured polythene bags, in the Sundar industrial estate around 45 kilometres (30 miles) southwest of the city centre.

Officials had earlier said the building was three-storeys tall.

Jam Sajjad Hussain, a spokesman for the rescue services, said 100 people were still trapped, 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.

The army meanwhile announced it was deploying specialist search teams and engineers to the factory.

Punjab chief minister Shahbaz Sharif said it was possible the building had been damaged after the October 26 earthquake.

"I have heard about earthquake affect on the building, but according to labourers the owner continued to build an extension," he told reporters.

 Poor safety record

 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.

Pakistan has a poor safety record in the construction and maintenance of buildings.

Last year, a mosque collapsed in the same city, killing at least 24 people.

More than 200 people lost their lives to collapsed roofs following torrential rainfall and flooding in 2014.

In 2012, more than 255 workers were killed when a fire tore through a clothing factory in Karachi, one of the deadliest industrial accidents in Pakistani history.

A judicial probe into the blaze was damning, pointing to a lack of emergency exits, poor safety training of workers, the packing in of machinery and the failure of government inspectors to spot any of these faults.

A murder case was registered against the factory owners, but it has never come to trial.