Two teams of fire brigade from Kishanganj while another one team from Thakurganj were pressed into service to douse the flames, SDO Mohammad Shafique said.
The fire fighters have brought the blaze under control, the SDO said.
Fire might have broken out due to short circuit, he added.
Construction Company Manager Santosh Singh said that "We have not assessed the actual amount of damage caused by the fire. The loss due to fire is being calculated," Singh said.
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Bihar Chief Minister Nitish Kumar had inaugurated the agriculture college last year before the announcement of assmebly elections.
The college, whose building is being constructed at Arrawari village under Pothia block of the district, is being run at Khagda Krishi Vigyan Kendra located in district headquarters.
Kumar had named the agriculture college after Dr A P J Abdul Kalam, the former President and eminent scientist of the country.