BEIJING, April 29 (Xinhua) -- China has returned over one million tonnes of maize imported from the United States that contained an unapproved transgenic component, the country's leading quality watchdog announced on Tuesday.

As of April 21, 1.124 million tonnes of corn and maize-based products contaminated with MIR162, a transgenic component yet to be approved by Chinese authorities, had been returned to the U.S., said Chen Xitong, spokesman of the General Administration of Quality Supervision, Inspection and Quarantine.

The administration has asked entry-exit inspectors nationwide to strengthen their monitoring efforts and have allowed them to return or destroy any agricultural products with unapproved transgenic components.

Chinese authorities found 183 batches of substandard food imports from 27 countries and regions and six shipments of substandard cosmetics in March, and rejected thm for the domestic market.