At least five people were killed and dozens of mostly women and children were trapped under rubble when a factory collapsed in Pakistan's city of Lahore on Monday, officials said.
The three-storey building used to manufacture veterinary medicines came crashing down when a gas explosion ripped through the premises, police said.
Rescue workers dug through the rubble with bare hands, desperate to answer trembling cries for help from people trapped beneath concrete slabs as sobbing relatives urged rescuers to do everything possible to recover their loved ones.
Police said the factory was illegal without the proper registration and that they were looking to arrest its three partners.
The accident at the 25-year-old factory was likely to highlight poor safety procedures among Pakistani manufacturers and with a 12-year-old boy among the dead, the use of child labour.
"Three bodies have been pulled out. Two are women and one a child. There are two other bodies of women still under the rubble," senior police official Ghulam Mehmood Dogar told AFP at the site.
"Eighteen people have been accounted for and 45 to 50 are still feared to be buried under the rubble," he added.
An AFP photographer said he saw the hand of a motionless woman lying under the rubble, who rescue officials said had died.
Rescue worker Mohammad Asif also put the death toll at five, saying that one boy and four women had been killed.
The rescue effort was hampered by narrow lanes in the congested Multan Road area, which made it difficult to get heavy machinery to the site.
"We're trying to deploy cranes to remove a very heavy concrete slab. Under that, we're still hearing cries for help. The workers were mostly women and children who were engaged in packing up the medicines," Asif told AFP.
Police said initially that a 12-year-old boy was killed.
Dogar told AFP that the cause of the disaster was "probably" the explosion of a boiler and of a gas cylinder.
Police were searching for three partners of the factory, but said so far there had been no arrests.
One slightly injured girl pulled out of the rubble was too frightened and panicked to tell reporters and rescue workers what she remembered.
Rescue workers used hammers, axes, chisels and shovels to shift the rubble to pull out injured, coated in dust as relatives stood by, sobbing.
Eight million people live in Lahore, 253 kilometres (160 miles) southeast of the capital Islamabad. It is considered Pakistan's cultural capital and perhaps the most liberal city in the conservative Muslim country.