WASHINGTON — A flurry of U.S. soybean and corn export business to China and “unknown destinations” presumed to be China finished off a week of healthy demand for U.S. grains by the world’s second largest economy.

The U.S. Department of Agriculture received reports from private exporters Friday morning that 1,440,000 tonnes of corn was bought for delivery to unknown destinations (viewed by the market as China) during the 2012-2013 crop year beginning Sept. 1, 2012.

The U.S.D.A. also announced a sale of 120,000 tonnes of corn to China in the current 2011-2012 marketing year ending Aug. 31, 2012.

Soybeans were also in demand on Friday. The U.S.D.A. reported private exporters sold 116,000 tonnes of soybeans for delivery to unknown destinations, again presumed to be China, in the 2012-2013 marketing year and 110,000 tonnes to China in the 2012-2013 marketing year beginning Sept. 1.

Earlier this week, U.S. exporters sold healthy amounts of corn and soybeans to China, as well as other countries. On April 25, the U.S.D.A. reported that private exporters sold 420,000 tonnes of corn to unknown destinations, believed to be China, for the 2012-2013 marketing year.

In addition, the U.S.D.A. confirmed Thursday a total of 265,000 tonnes of corn were sold to China, of which 90,000 tonnes were for the current 2011-2012 crop year and the remaining 172,500 tonnes were for the 2012-2013 crop year.

Wednesday the U.S.D.A. reported sales by private exporters totaling 480,000 tonnes of corn to unknown destinations, presumed to be China, for the current 2011-2012 crop year.

April 23, private exporters reported export sales of 165,000 tonnes of soybeans to unknown destinations, believed to be China, for the current crop year and 120,000 tonnes of corn for delivery in the 2012-2013 crop year, also to unknown destinations.

The recent trend has been for weekly corn and soybean U.S. export sales to exceed market expectations. In Thursday’s weekly U.S.D.A. export sales data for the April 13-19, 2012, period, both crops saw strong demand from overseas buyers. Net soybean sales for the week for 2011-12 and 2012-13 combined were 1,409,200 tonnes, above the high end of trade estimates. Net export sales of corn for both years during the week were 826,200 tonnes, within the range of trade estimates.