Residents transport their belongings to a temporary shelter after floods Wuhan, in China's Hubei province, on Tuesday. (Reuters)

Floods caused by heavy rains in northeastern China stranded tens of thousands of residents without power Wednesday as the worst flooding in more than a decade continued to besiege areas of the country.

Floods this year have killed at least 823 people with 437 missing and have caused tens of billions of dollars in damage, the State Flood Control and Drought Prevention reported.

More heavy rains are expected for the southeast, southwest and northeast parts of the country through Thursday.

About 30,000 residents in Kouqian town were trapped after torrential rains drenched the northeastern province of Jilin on Wednesday, the official Xinhua News Agency reported.

Water began flooding the town after the nearby Xingshan Reservoir and the Wende and Songhua rivers overflowed.

Flooding has hit areas all over China. In Wuhan city in central Hubei province, thousands of workers sandbagged riverbanks and checked reservoirs in preparation for potential floods expected to flow from the swollen Yangtze and Han rivers, an official with the Yangtze Water Resources Commission said Wednesday.

The Han is expected to rise this week to its highest level in two decades, Xinhua reported.

Though China experiences heavy rains every summer, flooding this year is the worst in more than a decade because the flood-prone Yangtze River Basin has seen 15 per cent more rain than in an average year, Duan Yihong, director of the National Meteorological Centre, said in a transcript of an interview Wednesday posted on the Xinhua website.

Thousands of rescuers in central China's Henan province searched for survivors Wednesday after a bridge collapsed from heaving flooding in the Yi River over the weekend, killing 37 people with 29 missing, Xinhua reported.

Floods have also put China's massive Three Gorges Dam to the test. On Wednesday morning, the dam's water flow reached 56,000 cubic metres per second, the biggest peak flow this year with the water level reaching 158 metres, Xinhua said, about 10 per cent less than the dam's maximum capacity.