Two provinces declared states of emergency in a bid to combat the worst flooding along the Yangtze River in four decades.
Authorities in Jiangxi made the decision after a dyke was breached for the first time since 1954.
Anhui also announced an emergency, asking people to give top priority to flood relief work.
A flood control official in Jiangxi said: 'We are in an emergency situation. All materials can be requisitioned for flood control.' The official said 10,000 cadres had been deployed to patrol a 13km dyke separating the Yangtze from Saicheng Lake, near Jiujiang.
If the swollen river burst through the dyke it would affect 240,000 people living behind it as well as 24,000 hectares of farmland, said Yong An village party secretary Nie Zhieinp.
Mr Nie said 6,700 residents were mounting round-the-clock vigils in groups of 10, sheltered in makeshift huts set every 500 metres along the dyke. Patrolmen discovered a 2cm breach in the dyke late on Sunday but managed to repair it.
Xinhua reported that Jiujiang, located next to a sharp bend in the river, was in serious danger. 'We predict the water level in Jiujiang will reach 23 metres on Wednesday,' said one official. 'It has already exceeded the record.' The city's dykes can withstand a maximum 23.25 metres.
