More than 21 million people are affected in Anhui province alone with economic losses put at 4.8 billion yuan (585 million dollars).
Several controlled explosions on dikes on the Huaihe river in Anhui occurred Sunday to release water that has been rising since late June into flood diversion areas, the Xinhua news agency said.
The raging torrents of water submerged roads and farmland, but there was no information on whether property had also been swallowed.
A flood control official told AFP that at least five people have died from the floods so far and more than 5,000 had been injured or had come down with disease.
"Until now five people have been killed and 5,371 people have either been injured or have got disease," said Wang Hua, an official in the disaster relief section of the Anhui Department of Civil Affairs.
"370,000 people have been relocated. These people lived in the areas threatened by flooding or in the flood discharge areas.
"21 million people (in Anhui) have been affected by the flooding of which 14 million are seriously affected," he said, adding that millions of hectares of farmland had been ruined.
"Economic losses are 4.8 billion yuan, of which 3.8 billion is in agriculture," he said.
The river has been running at more than 26 metres (86 feet), prompting President Hu Jintao to wade into the drama, demanding that dikes must not be breached.
He told the country's top flood control officials "to give top priority to the protection of people's lives during the ongoing fight against floodwaters" and to do everything possible to prevent the outbreak of disease.
Thousands of soliders have been thrown into the fight to strengthen dikes along the Yangtze river and other stretches of the threatened Huaihe, a tributary of the Yangtze.
According to Xinhua, many of those evacuated, which they put at 200,000, are living in makeshift shelters in schools or factories and a massive relief effort has swung into action to provide food, medicines and tents.
A state of emergency was declared at midnight Friday in the region where, according to the weather service, rain will continue until July 10.
Heavy rains are affecting large swathes of China.
