The number of deaths from an outbreak of Japanese encephalitis in India's Uttar Pradesh state has risen to at least 175.
Children are worst affected by the outbreak
Officials fear the death toll may be much higher as fatalities in rural areas often go unreported.
They say there is an acute shortage of vaccine in the northern state.
In the past few weeks more than 500 people, mostly children, have been treated for the disease, which occurs regularly during India's monsoon.
Encephalitis, a mosquito-borne disease, has killed 8,000 people in Uttar Pradesh since 1978.
The BBC's Ram Dutt Tripathi in Lucknow says the official figures may be under-estimates as Gorakhpur district, 250km (165 miles) east of state capital Lucknow, has itself reported 167 deaths.
Most of the victims are very poor people from rural areas, says Dr TN Dhole, professor of microbiology in Lucknow's Sanjay Gandhi Post Graduate Medical Institute.
Senior officials have travelled to the area to supervise relief operations.
Doctors said children between the age of six months to 15 years were worst-affected.
Dr KP Kushwaha, a paediatrician from Gorakhpur, said up to 50 new sufferers were arriving every day.
He said there were no beds available in the hospital and even the corridors were full.
Japanese encephalitis, which causes high fever, vomiting and can leave patients comatose, usually hits the state at the end of August but this time it struck in July.
The disease has recurred annually in eastern regions of the state since about 1980.
Uttar Pradesh needs 50m vaccines every year, according to state health officials.
But the Kasauli-based Central Institute is only able to supply 200,000, they say.