More than 50,000 people have been moved from their homes in on China's border with North Korea, after the Yalu river burst its banks in heavy rain.
Some 200 houses have been destroyed in the city of Dandong, and three people are reported missing, state media says.
Flooding has also been reported across the border, with the North Korean city of Sinuiju severely affected.
More than 1,500 people have died in China in recent months during one of the country's wettest-ever summers.
In Dandong, floodwater caused a dyke to burst triggering severe flooding in an industrial area. The main railway line out of the city is also reported to have been cut off.
Some 51,000 residents have been taken to higher ground.
In Sinuiju in North Korea, more than 30cm [12in] of rain is reported to have fallen overnight.
The swollen Yalu river - known as the Amnok in North Korea - burst its banks and swamped houses, public buildings and farmland in five villages near the city, Pyongyang's official news agency said.
Armed forces are assisting with the rescue effort, the KCNA agency reported.
Sinuiju lies on a vital trade route for North Korea and previous flooding has exacerbated problems in a country where millions have died in famines over the last two decades.
In China the latest flooding comes after the deaths of more than 700 people in a landslide triggered by heavy rains in Zhouqu county, Gansu last week.
China's state weather bureau is forecasting more heavy rain throughout the weekend.