The explosion in the oil tank took place following a leakage in the boiler, they said.
It took five hours for fire brigade personnel from Hisar, Tohana, Barwala and Narwana to extinguish the fire. The impact was so powerful that the roof and walls of the mill crumbled and it soon turned into a heap of debris.
All the injured were shifted to Hisar and were admitted to different private hospitals.
Seven people -- Rahul, Pankaj Ram, Suresh, Bhim Raj, Ganesh, Ramesh and Narender received burn injuries ranging from 90 per cent to 100 per cent, police said.
Their condition is stated to be the critical, said police.
Eight labourers received 20 per cent to 85 per cent burn injuries and have been admitted to private hospitals in Hisar. The police chief of Hisar district, Manisha Chaudhary visited the spot and hospitals to take stock of the situation. The incident comes close on the heels of an boiler blast in the NTPC plant in UP which left 33 persons dead.