Houston - Ship movement along the Mississippi River south of New Orleans stopped on Saturday as powerful Hurricane Gustav churned toward the Louisiana coast, and port operators made last-minute preparations.

The landfall location for Gustav, now a Category 4 hurricane with top winds of 150 miles per hour (240 kph), was still uncertain, but forecasters said Gustav was likely to near the central Louisiana coast by late Monday or early Tuesday.

In anticipation of Gustav, the Mississippi River was shut to all ship traffic between the Gulf of Mexico and New Orleans as 6 p.m. CDT (2300 GMT) on Saturday, ship pilots said.

At the Port of New Orleans, Chief Executive Gary LaGrange said, "With Gustav still not in the Gulf, it's hard to gauge what impact Gustav will have on the port, but we have taken the necessary precautions to protect people and property."

The larger Port of South Louisiana, just up the Mississippi River from New Orleans, was also preparing for the storm. It suffered significantly less damage than the Port of New Orleans in Hurricane Katrina in August 2005.

New Orleans' port was devastated as a result of Katrina. Port officials estimated the storm inflicted $100 million in damage, while businesses dependent on the port suffered up to $300 million in losses.

Before Katrina, the New Orleans port accounted for a fifth of U.S. export and import trade. It was also the main outlet for U.S. agricultural exports, handling barges of wheat, soybeans and corn shipped from the American Midwest.

Elsewhere along the Gulf Coast, ports and ship-handlers were making plans.

Pilots at Lake Charles in west Louisiana, and Sabine Pass in east Texas, made plans to halt traffic. Ports from Houston to Mobile, Alabama, were bracing for storm conditions.

The Port of New Orleans set up an alternate operations center in northwest Louisiana at Shreveport.

The port planned to finish with container vessels and then to lock down its gantry cranes on Saturday. Ships handling steel, metals, poultry and other products were finishing up work.

While some vessels were departing the port, a number were expected to seek shelter at New Orleans, port spokesman Chris Bonura said.

While New Orleans is at the southern end of Louisiana where the Mississippi River snakes its way into the Gulf of Mexico, the 2,000-acre (809-hectare) port of Shreveport-Bossier is in the northwestern corner of the state with links to highways, railways and airport facilities.

(Reporting by Bruce Nichols; Editing by Peter Cooney)