The government asked people living along the river bank to vacate their huts and houses and not to venture into the river.
"There has been very heavy rainfall close to Daltonganj in Palamu district of Jharkhand. The water is now moving through Koel river towards Sone. We are expecting around 3 lakh cusec water to reach Indrapuri barrage in Rohats district in Bihar tonight," said Disaster Management Department Officer on Special Duty (OSD) Vipin Kumar Rai.
As a result the water level in Sone river may shoot up suddenly and endanger the people living close to it or those who have settled in parts of the river bed. It could also harm those who enter the river, especially the fishermen, he said.
The OSD, however, clarified that the alert is not about flood and there is no reason for people staying in the four districts to panic.
Sone flows through the southern parts of Bihar and merges in the Ganga at Koilwar in Bhojpur district.