People living in communities surrounding a large shallow lake have been overrun by field mice after floodwaters drove the rodents out of islands on the lake, state media reported Monday.

The mouse invasion began on June 23 when the Yangtze River flooded, raising the water level in central China's Dongting Lake and submerging mouse holes on lake islands, the official Xinhua News Agency said.

Now, an estimated 2 billion mice are ravaging crops in 22 counties around the lake, and authorities were rushing to construct walls and ditches to keep the rodents out. Residents have killed more than 2.3 million field mice - or 90 tons of the rodents, Xinhua said.

In Hunan province's Yiyang County, a ditch along the lakeshore was filled with mice. Residents were using clubs and shovels to beat them to death, while others scooped the furry animals out using fishing nets.

Mice have already damaged dikes and ruined crops in areas where authorities were slow to build walls and ditches, Xinhua said.

The rodent problem was expected to worsen as more floods were forecast for the upper reaches of the Yangtze River and Dongting Lake.