The girls were digging a pit near a river on the outskirts of Maksudpur village under Minapur police station in Muzaffarpur district, police said.
The victims were identified as Abhilasha Kumari, 16, Suman Kumari, 12, and Asha Kumari, 12. "Three of them died after soil collapsed on them suddenly," police official Jitendra Prasad told IANS over telephone.
The villagers later dug out the bodies of the victims.According to police, two other girls were injured in the accident and admitted to a government hospital.