Rescue workers in Pakistan struggled into the night to reach dozens of people still trapped in the ruins of a factory that collapsed Monday, killing at least nine people.

Police said they believe the three-story factory, which produced veterinary medical products in the eastern city of Lahore, caved in after a gas cylinder inside exploded. Some 60 people were inside the factory at the time of the incident. Several women and young children were among the casualties.

Emergency workers so far have rescued at least 13 people, but they say their efforts have been hampered by the narrow streets around the factory slowing the arrival of heavy machinery at the site.

Authorities say the factory had been ordered closed. It was not immediately clear why it was ordered shut or why it was operating despite the closure order.