ISLAMABAD, Feb. 29 (Xinhua) -- An accidental boiler explosion in a paper factory has left four laborers killed and five others injured in Kasur district of Pakistan's east Punjab province on Saturday, local police said. The laborers were working at early shift when the boiler exploded due to some technical fault, killing and seriously injuring all the nine people working around it, while the laborers working in other parts of the factory remained safe due to timely extinguishing of the fire. Part of the factory got damaged in the explosion, and investigation is underway to determine the exact cause of the blast. The injured people have been shifted to a nearby hospital and three of them were in critical condition.  Enditem