Story highlights

NEW: Six dead, eight rescued from factory explosion

NEW: As many as 49 people remain in the rubble, a police official says

Authorities suspect a boiler explosion caused the building's collapse

Islamabad, Pakistan CNN  — 

At least six people are dead and as many as 49 possibly trapped after a factory collapsed in Pakistan on Monday, police said.

Eight people have been rescued from the rubble of the veterinary medicine factory, said Sarfraz Falki, a Lahore police official. Falki said 63 people were in the building when it collapsed, and rescue workers were continuing to try to reach any survivors. Authorities earlier had said 43 people were in the building when the explosion happened.

Muhammad Salim, a Lahore police official, said the building apparently collapsed because of a boiler explosion.

In Pakistan, boilers are usually old and large, and building regulations in Pakistan are weak and often go unenforced, critics have said.