At least eight workers were killed in a blast in a quarry in Andhra Pradesh's Kurnool district on Friday, police said.Another eight workers were also injured in the incident that took place in Hathi Belgal village in Alur 'mandal' (block) of Kurnool district.The injured were admitted to the government hospital in Alur, where the condition of three is stated to be critical.About 20 workers belonging to Odisha were believed to be in a shed when the blast occurred. The police suspect that some more workers could be trapped inside.A fire which broke out with the blast engulfed the shed. Three tractors, one lorry and two sheds were destroyed in the fire.The huge blast also damaged a few houses near the quarry.The blast which was heard at a distance of more than 10 km sent panic among the residents. The cause of the blast could not be known immediately.