China's Tianjin municipality has returned a batch of corn shipment tainted with a genetically-modified (GM) strain not approved by the country's agriculture ministry, the local quality watchdog said.

The 21,800-tonne shipment from the United States was to be used as animal feed but was found to contain the unapproved MIR162, a strain of insect-resistent transgenic corn, said an official with the Binhai branch under Tianjin Entry-Exit Inspection and Quarantine Bureau.

China found the first batch of MIR162 tainted corn shipment last October in Shenzhen in south China's Guangdong Province, and detected several other batches at the country's ports. This was the first case in Tianjin.

Statistics released by the General Administration of Quality Supervision, Inspection and Quarantine, the country's leading quality watchdog, showed that China rejected 601,000 tonnes of unapproved GM corn imports in 2013.