15-year-old Shefali Khatun and two minor boys, one of who hails from the neighbouring South Dinajpur district, died at the paediatric ward of the district hospital yesterday.
According to hospital sources, at least 200 patients are admitted in the medical ward and there is a rush of patients in the paediatric ward also.
Blood samples have been sent to Kolkata for diagnosing the disease, officials said.
It is suspected that the mysterious fever can be dengue. The symptoms include high body temperature, body ache and nausea.