HOUSTON (Reuters) - The U.S. Coast Guard said it had reopened a nine-mile (14-km) stretch of the Mississippi River near Baton Rouge, Louisiana, to southbound traffic on Tuesday afternoon.

A total of 49 southbound ships were waiting to transit that section of the river, shut since Friday when three barges sank.

Southbound ships face tight restrictions when sailing down that portion of the Mississippi, which is near record-high flood levels at Baton Rouge. Ships may only move through that part of the river during daylight hours.

The Mississippi is the key waterway for grain exports, 60 percent of which move down the river from the U.S. Midwest to the Gulf of Mexico.

Eight Louisiana refineries dependent on the river to bring crude oil from the Gulf of Mexico and to move refined products into the Gulf were not affected by the closure, which occurred north of those plants. The docks at Exxon Mobil's Baton Rouge plant had already been shut due to the high water.

(Reporting by Erwin Seba; Editing by Gary Hill)