Indian health officials say the death toll from an outbreak of Japanese encephalitis in northern Uttar Pradesh state has reached nearly 600, with most victims being children.

State health officials say they fear the actual death from the mosquito-borne disease might be much higher because many deaths in rural areas are not reported.

They say the epidemic has spread to 27 districts in Uttar Pradesh and to neighboring Bihar state. The doctors say vaccination is the only way to halt the spread of the illness, but state authorities do not have enough stock.

Meanwhile, officials in neighboring Nepal say the disease - that causes the brain to swell - has killed at least 172 people and sickened hundreds more in the Himalayan kingdom since April.

Some information for this report provided by AP.