Almost 600 people have now been officially declared dead in an outbreak of Japanese encephalitis in India.
Over 100 deaths have been reported in the past 24 hours
Officials fear the actual death toll might be much higher because many deaths in rural areas are not reported.
The disease has spread to more than 27 districts in Uttar Pradesh, including the state capital, Lucknow, and to neighbouring Bihar state and Nepal.
Encephalitis, a mosquito-borne disease, has killed at least 8,000 people in Uttar Pradesh since 1978.
Officials told the BBC that many field medical officers were not accurately reporting the death toll in their areas for fear of being punished for failing to take sufficient action to stop the spread of the disease.
Meanwhile an outbreak of dengue fever has claimed 15 lives in the eastern Indian state of West Bengal.
"The situation is tough. Fifteen people have died and almost 900 are suffering from dengue," Prabhakar Chatterjee, the state's chief health officer, told Reuters.