The ministry didn't disclose why there were rejected but said the number was too high even in light of the fact that South Korean products made up some 65 percent of China's seasoned laver imports.

South Korean exporters complain that China has an excessive permissible limit for germs in seasoned laver products, which have a low risk of bacterial propagation because of their high temperature processing.

According to the ministry, China is the only country in the world that has such a rule.

Market watchers voiced concerns that China may toughen its customs clearance for South Korean seasoned laver, given its escalating economic retaliation against South Korea over the deployment of a Terminal High Altitude Area Defense battery.

"Some exporters say that China seems to be strengthening customs clearance procedures for South Korean seasoned laver recently, though only one shipment was rejected in January," a ministry official said. "We are keeping close tabs on the issue."

South Korea exports of seasoned laver to China spiked 124 percent on-year to $64.9 million in 2016, with overall shipments of dried seaweed gaining 15.9 percent to a record high of $353 million.

China has slapped a series of economic sanctions on South Korea after Seoul finalized a deal last week with Lotte Group to station the missile defense system on a Lotte golf course in the southeastern county of Seongju.

China has ordered travel agencies to stop selling group tours to South Korea and suspended operations of more than 50 Lotte Mart stores in the country, with analysts fearing more retaliatory measures are yet to come.

Seoul and Washington say the anti-missile battery is meant to better counter missile threats from North Korea, while China insists America will use the high-powered radar that comes with the system to spy on its military. (Yonhap)