Coast Guard says Mississippi River closed near Natchez

A building is seen partially submerged as floodwaters approach Simmesport, Louisiana May 16, 2011.

HOUSTON (Reuters) - The key waterway for grain exports was cut off on Monday when the U.S. Coast Guard closed the Mississippi River near Natchez, Mississippi.

The Coast Guard said 15 miles of the Mississippi was closed to all traffic to protect ships and flood control structures because flooding has raised the river to record levels.

Two vessels were waiting to move northbound on the river by the closure and one ship was waiting to move southbound, the Coast Guard said.

About 60 percent of U.S. grain exports go out through the Mississippi.

Eight Louisiana refineries dependent on the river to bring crude oil from the Gulf of Mexico and to move refined products into the Gulf, are not affected by Monday's closure.

The Coast Guard gave no estimate for when the River would re-open.

Weeks of heavy rains and runoff from an unusually snowy winter caused the Mississippi River to rise, flooding 3 million acres (1.2 million hectares) of farmland in Mississippi, Tennessee and Arkansas and evoking comparisons to historic floods in 1927 and 1937.

The bulge of water released by those rains was still upriver and making its way toward Louisiana. In Vicksburg, Mississippi, the Mississippi River's height swelled to 56.3 feet, eclipsing the record set in 1927.

(Reporting by Erwin Seba; editing by Carol Bishopric)