Authorities in Kanagawa Prefecture say they have begun discharging water from the Shiroyama Dam, starting at 9:30 p.m.
It's an emergency measure to prevent the dam from overflowing.
The release will cause the water level in the Sagami River and its tributaries to increase, and authorities are urging residents in the following municipalities in Kanagawa Prefecture to be on alert:
The cities of Sagamihara, Hiratsuka, Chigasaki, Atsugi, Ebina, Zama, and the towns of Samukawa and Aikawa.
Officials are calling on people to avoid getting too close to the riversides and to act with caution.