Officials said 11 deaths had been reported in Bihar in the last two days, taking the toll in six weeks of flooding across the state to 142.
"There is waist-deep water in the basement of our apartment and our vehicles are virtually submerged," said Ramesh Prasad, a resident of Patna's Kurji district.
Floods regularly hit Bihar during the June-September monsoon season as the Ganges and its tributaries, many of which flow in from neighbouring Nepal, breach their banks.
State Relief Minister Ram Vichar Rai said hundreds of thousands of people had been displaced because of floods in 19 of Bihar's 38 districts this year.
The Ganges, along with its tributaries the Son and the Punpun, were all flowing above danger levels and authorities were strengthening embankments on the outskirts of Patna to prevent water entering the city, officials said.
Fifteen people were killed and thousands displaced on Tuesday in Madhya Pradesh state, Bihar's neighbour to the south, as the Son inundated several eastern districts of the state.
Hundreds of people were camped out on road embankments and other high ground, one resident said.
The annual rains are crucial to India's farming-dependent economy but too much rain triggers floods that regularly displace millions and kill hundreds of people.
- Reuters - Thomson Reuters Foundation
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