A quarry in central Thanh Hoa Province suddenly collapsed on Friday morning, killing three workers and injuring one, authorities reported. The collapse occurred at about 6 am on June 7 in the Vuc Mountain area in Dong Quang Commune, Dong Son District, where the quarry is located. The dead victims are identified as Pham Van Su, 46, Nguyen Dinh Nam, 33, and Hoang Dac Long, 28. All the three were killed on the spot when a large volume of rocks, estimated at tens of cubic meters, rolled down the mountain and buried them.  The injured worker in the deadly incident is Lam Ba Lang, 51, who was taken to Thanh Hoa General Hospital in critical condition.    These four victims, all of Thanh Hoa, had been employed as non-contract workers by the quarry’s developer, Song Ma One-Member Co Ltd, for more than a month. The company, whose office is located in Thanh Hoa City, has assigned its branch No. 5 to manage and operate the quarry. The bodies of the dead victims have been brought back to their home for burial.  Local police have examined the scene and are investigating the cause of the accident.   Two years ago, a heart-breaking quarry collapse also occurred at Len Co Mountain on central Nghe An Province on April 1, 2011, killing 18 workers and severely injuring 6 others. These victims were buried under about 1,000 cubic meters of rock.