With farmers moving to cities amid fast urbanization, China has 7.6 million hectares of idle land that could be used as farmland and land for construction, a study has found.

"One-fourth to one-third of land in traditional agricultural regions is not in use, being occupied by empty houses and abandoned farmland," said Liu Yansui, author of the report and a researcher with the Institute of Geographic Sciences and Natural Resources Research under the Chinese Academy of Sciences.

The number of rural residents could fall to 280 million by 2020, from 300 million now, according to the report issued on Monday.