Additional Deputy Commissioner of Police (Assansol) S Ganguly said three persons had illegally entered the ECL mine at Salanpur which the ECL was not using at present.
The three died as the pit of the coal mine collapsed, the ADCP said.
The three have been identified as Mohan Barui (48), Purna Chandra Barui (55), Ajit Barui (45), the sources said adding that the bodies have been sent to hospital for postmortem.