Islamabad, Pakistan (CNN) -- The death toll rose to 15 as rescue workers continued to look for victims Tuesday inside a factory that collapsed in Pakistan.
A boiler explosion apparently caused the veterinary medicine factory to collapse Monday, said Muhammad Salim, a Lahore police official.
In Pakistan, boilers are usually old and large, and building regulations in Pakistan are weak and often go unenforced, critics have said.
About 120 rescue workers were at the scene Tuesday, looking for survivors who may still be trapped in the building's rubble, according to the Associated Press of Pakistan.
The 15 dead are comprised of 12 women and three men, the news agency said.