The incident took place when the victims were trying to open a carton box found on the verandah of their house at Dahapada under Sahadev Khunta police station limit late last night and it exploded, police said.
Under the impact of the blast, Sanjulata Pradhan, her daughter Sharmista Pradhan and their relative Josabanta Pradhan sustained critical injuries.
They were taken to Balasore district headquarters hospital and then shifted to SCB Medical College and Hospital at Cuttack, they said.
Investigation into the incident was in progress to ascertain the circumstances in which the box was kept on the spot, police said.
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