Police said no arrests could be made though an FIR filed against unnamed persons for damaging hospital property and causing panic among other patients and relatives.
Police said the 11-year old Dhananjoy Halder had been taken to the nursing home on Tuesday last and operated at around 2:30 pm on that day.
He slipped into coma later on and had to be shifted to another private hospital by the poor parents.
The mob, which demanded return of Rs 15,000 the hospital took as surgery cost for the patient, left after a big police force reached the spot.
Tension remained in the area.