The flood situation continued to remain grim in Bihar's Gopalganj, Siwan and Saran districts on Monday after the Gandak river overflowed its banks, affecting thousands of people.
More than five lakh people are under threat as the water spreads, destroying standing crops and forcing people to flee their homes.
"The overflowing water of the Gandak river has entered dozens of villages and is flowing at some places on National Highway 28 that disrupted road traffic," an official of the water resource department said.
Chief Minister Nitish Kumar is undertaking an aerial survey of flood-affected districts on Monday.
The Gandak overflowed after Nepal released over two lakh cusecs of water into the river following heavy rains in the Himalayan republic. The main embankment was breached last week and more breaches occurred on Sunday.
The principal secretary of the disaster management department, Sri Vyasji, said the government decided to set up mega camps in affected areas.
A district official said the threat of flood looms large over dozens of other villages, creating panic among thousands of residents.
Hundreds of people have fled their homes and the state government has asked those living in low-lying areas to shift to safer places.
Rescue and relief operations have been intensified. A team of the National Disaster Response Force has been rushed with motorboats to help those trapped in flood waters, the official said.
In 2008, more than three million people were rendered homeless in Bihar when the river Kosi breached its bank upstream in Nepal and changed its course.