The 3.1km-long bridge was being constructed by SP Singla Constructions Private Limited at a cost of Rs 1,710 crores.
However, no casualties were reported in the incident.
The Bhagalpur administration said superstructure spanning 100 feet between pole numbers 4 and 6 from the Sultanganj end collapsed owing to the impact of strong winds and rains in the intervening night of Friday and Saturday.
Meanwhile, Bihar Chief Minister Nitish Kumar has ordered an inquiry into the matter.
The bridge is one of the most ambitious projects of the Bihar government. The foundation stone of this bridge was laid by Nitish Kumar at Parbatta in Khagaria district on February 23, 2014. The under-construction bridge will link south and north Bihar.
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