The labourers had been employed by a contractor illegally in the mine that had been closed by a government order, Rajauli Deputy Superintendent of Police (DSP) Sarfur Rehman said.
The deceased has been identified as Rajendra Chandravanshi, he said.
"The contractor was indulging in stone mining in Baudi village in Rajauli area without government permission. He had employed several labourers for the purpose. Two labourers were injured when the piece of rock fell on them," said the DSP.
The police has sent the body for post-mortem. So far no arrest has been made, he said.