An estimated 400-450 fell ill in past few days alone in the Madarihat, Kalchini and Dhupguri blocks of the district, the sources said.
The symptoms confirmed chikungunya outbreak which is caused by Aedes aegypti mosquito due to the habit of labourers of tea garden to keep stored water for drinking as stagnant water gives birth to the larvae.
A medical team went to the area.
The ailing persons had been taken to local health centre, hospitals.
Though unconfirmed reports said eight deaths had been reported in the area in May-June, the health department did not confirm any death as caused by any mosquito-borne disease.