About 95 percent of the world's white cranes, half of the white-naped cranes and 60 percent of swan geese are believed to migrate to a nature reserve at Poyang Lake each year in Jiangxi province, Xinhua news agency said.

Hundreds of workers at the reserve distributed grain, corn and vegetables but found only 40,000 birds, leaving about 100,000 unaccounted for, said Luo Shengjin, deputy director of the reserve.

The worst weather in decades hit large areas of China last month, killing at least 107 people and causing more than 15 billion dollars in economic losses, according to official figures.