A three-story factory collapsed Monday in the Pakistani city of Lahore after a gas explosion, killing at least three people and trapping dozens, emergency officials said.

The factory has completely collapsed and two houses next to it as well, an emergency official at the site told Reuters by telephone, adding authorities were having trouble getting heavy rescue machinery to the area because of narrow streets.

Karamat Ali, a spokesman for the government Rescue 1122 emergency service, said three dead, including a 10-year-old boy, and 13 survivors had been pulled out of the rubble.

He said 17 women and 45 men were at work when the factory, which produced veterinary medical products, crumbled. The death toll was expected to rise.

The incident is likely to raise fresh questions about Pakistan's industrial safety. Building and zoning regulations are weak and often not enforced, critics say.

A senior city official said the factory should not have been operating.

The factory was supposed to be sealed. We will investigate why it was still running, city official Ahad Cheema told reporters.

It was not clear why it had been ordered sealed.

Pakistan's government is often described by opponents as too corrupt and inept to tackle an array of problems, from struggling industries to Taliban insurgents who carry out suicide bombings across the South Asian nation.

My house is near the factory. I felt a strong jolt and my house shook. I thought it was a bombing, said Awais Raza.

Emergency workers and residents were shifting rubble by hand as authorities struggled to move a large crane to the site to help with the rescue.

We are looking for voids in the destruction where there are likely to be survivors, Rizwan Naseer, head of Rescue 1122, told reporters at the site.

(Reporting by Mubasher Bukhari in LAHORE and Qasim Nauman in ISLAMABAD; Editing by Robert Birsel)