BEIJING - Concerns have been expressed by a senior Chinese official about the country's grain security as rapid urbanization is squeezing room for further increase in output.

In an interview with Xinhua on Monday, Minister of Commerce Chen Deming said grain supply is in tight balance with demand, though the country has recorded consecutive harvests over the past nine years.

Chen said tight supply is a challenge for the whole world and will persist because of rising crude oil prices, global warming and conversion of grain into fuel.

Rapid urbanization has led to a decline in arable land areas and a large number of rural labor forces switching to non-agricultural jobs are key factors hindering China's grain output.

To guarantee grain security, the Chinese government has set a "red line" demarcating that its arable land never drops below 1.8 billion mu (120 million hectares) and it has stepped up efforts to boost modern agricultural development.