At least seven migrant workers were killed and around 15 others were injured after a massive rock collapsed at a stone quarry in Bengaluru on Thursday.According to the police, the labourers belonged to Bihar and West Bengal. The incident took place at a stone crusher unit in Madapatna in Bengaluru South taluk while the workers were engaged in quarrying operations. The identities of the deceased are yet to be established. Around 15 others sustained injuries and were shifted to a private hospital for treatmentA police official said the accident occurred around 7.30 am at Kaveri Jelly Crusher in Bengaluru South taluk, adding that the boulder fell on the spot where workers were operating machinery, leaving them with no time to escape.Prime Minister Narendra Modi, President Droupadi Murmu and Chief Minister DK Shivakumar expressed grief over the incident, and offered their heartfelt condolences to the bereaved families.According to the police, the quarry belongs to a man identified as Anandaswamy, who has been taken into custody for questioning. They said a case is yet to be registered, and the exact cause of the rock collapse is under investigation.”The bodies have been recovered, and senior officers have visited the spot…it is yet to be determined whether the quarries were operating legally or illegally. The prescribed rules must be followed,” the Chief Minister said.