"Some cargoes simply berth offshore and buyers are not unloading the cargoes before testing results are complete."
The U.S. corn market appeared unaffected by China's rejection. Chicago Board of Trade March corn futures were up 2 cents at $4.29-1/2 a bushel late Wednesday morning. Prices have increased 4.2 percent since China's first rejection in November.
Large volumes of the rejected corn have been snapped up by importers in other Asian countries, sometimes with price cuts, European traders said.
China expects a record corn harvest this year and faces a massive glut due to weak consumption by the animal feed industry.
Its corn output in 2013/14 is likely to rise 5.9 percent on the year to a record 217.7 million tonnes, surpassing consumption, seen at 197 million.
The country's corn consumption fell 1.1 percent from the previous year, partly due to outbreaks of bird flu early in 2013, the China National Grain and Oils Information Center (CNGOIC) says.