A top Chinese agriculture official backed measures to prevent farmland grabs in China, warning that the country's waning self-sufficiency will make it increasingly dependent on imports to feed itself.

Chen Xiwen - deputy director of the Chinese Communist Party's leading group on rural policy – said China had to better protect its arable land, and boost farm productivity, to improve an agriculture sector which has struggled to keep up with the country's booming economy.

China would need an extra 40m hectares of arable land - an area the size of Zimbabwe and some 25% of the existing total – to grow enough crops to replace imported volumes.

China, famously, has to support about one-fifth of the world's population with less than 10% of global arable land.

However, current land rules have failed to protect farmland for agriculture, a factor which, with the migration of as many as 230m farm workers to cities so far this century, has undermined China's production potential.

'Expropriated too much'

The comments come the day after China's cabinet voted to tighten laws against land grabs, warning over the threat to food security besides its impact on fuelling rural unrest.

"Rural land has been expropriated too much and too fast as industrialisation and urbanisation accelerate," a meeting of the State Council said, according to the official Xinhua news agency.

"The government must make efforts to beef up support for farmers and place rural development in a more important position."

And earlier this month, Han Changfu, the Chinese agriculture minister, warned over the need for broad agricultural reform, given challenges such as water shortages too.

'Greater risks'

"The next five-to-10 years are a key period for the development of China's agriculture sector - with production factors like land, water and labour getting tighter," Mr Han told the Communist Party Congress.

"Agricultural production is facing greater risks - natural risks, market risks, security risks - and it is entering a period of high investment, high costs and high prices."

Improving Chinese production would mean encouraging a "new type of agricultural player and develop large-scale mechanised farming", in contrast to the current sector predominated by small farms, relying to a high degree on manpower.

The comments come as Hu Jintao, the Chinese president, prepares to hand over power to his successor, Vice-President Xi Jinping.

'Story of their economic growth'

China's growing reliance on imports has been highlighted by data for the first 10 months of the year showing a near-quadrupling, to 1.98m tonnes, in imports of rice, a grain in which the country has been largely self-sufficient.

China has been a net importer only seven times in the last 50 years – three of them being the last three years, according to US Department of Agriculture estimates.

The country has also become a net importer of corn, and this year a big buyer of wheat too.

Macquarie analyst Chris Gadd, flagging "strong demand from China for high quality milling wheat", said that the country's "drive for high quality wheat in China is a story of their economic growth.

 "As their populous becomes more affluent they have a greater demand for higher-quality baked goods such as speciality breads along with pastries.

"This shift will drive a great requirement for high quality wheat," he said, if downplaying expectations for wheat imports in 2012-13.