The blast took place when the labourers were filling a trench dug up for installing explosives in the mine in Billi Markundi and lightning struck , SDM Sadar , Kailash Singh said.
They have been admitted to Community Health Centre from where five seriously wounded have been shifted to district hospital, he said.
As many as 17 laboureres were working in the mine at the time of the blast, he said.
Meanwhile, the district administration has announced an ex-gratia of Rs 5 lakh to the next of the kin of each deceased.