"The cause of the spike in cases is still under investigation, but the symptoms are dengue-like", Amit Mohan Prasad, the state's additional chief secretary (health), told India TV.
Schools will remain shut until 6 September for students in grades 1 through 8.
Seventy people, including 12 children, were reported to have died due to the mysterious disease. Uttar Pradesh Health Minister Jai Pratap Singh, however, denied the reports, stating that 32 children and seven adults had died.
Most fever carriers suffered from high temperatures, dehydration, and a low platelet count. Symptoms similar to dengue, such as fever, severe headache, muscle pain, nausea, and enlarged lymph nodes, have been detected in some of those infected.
Dengue fever is a mosquito-borne viral infection that is widespread in Southeast Asia. There is no specific treatment for the disease, and only those who have already had the disease can be vaccinated against it. The global incidence of dengue has grown dramatically in recent decades. About half of the world's population is now at risk. There are an estimated 100-400 million infections each year, according to the World Health Organisation.