Millions of residents in Louisiana on Saturday braced for Tropical Storm Barry, which lashed the southern US state with strong winds and heavy rain as it edged towards shore at near-hurricane strength.

Governor John Bel Edwards said Louisiana’s largest city New Orleans was well prepared to withstand the storm, but urged vigilance by residents across the state, as authorities called on people to stay off the streets.

“No one should take this storm lightly,” Edwards said on Twitter.

Authorities ramped up evacuations, airlines cancelled flights and flood gates slammed shut as the National Hurricane Center (NHC) forecast the storm would reach hurricane status before making landfall along the US Gulf Coast.

By the Saturday afternoon the storm was packing winds of 115 kilometres an hour − just below hurricane strength − and was located about 80 km from Morgan City, to the west of New Orleans.

In Morgan City, the streets were empty as heavy rain fell. The Atchafalaya River had flooded its banks, and trees were already blown over in residential areas.

The storm was only moving at five miles an hour, meaning landfall could be a while off.

“It’s painstakingly slow,” government meteorologist Ben Schott told CNN, noting that residents should not be lulled into complacency about facing the storm.

“If you don’t have to go anywhere, stay home. Monitor what’s going on. Do not put yourself at risk.” With Barry threatening massive rainfall across several southern states, federal emergency declarations were issued to help free up resources to address the storm.

For many, the large storm swirling in the Gulf of Mexico and the potential for large-scale flooding in coastal and river areas has brought with it unpleasant memories of 2005’s deadly Hurricane Katrina.

Thousands have packed up and left their homes as flood waters hit low-lying areas like Plaquemines Parish, where road closures left some communities isolated.

Dozens took shelter in Plaquemines’s Belle Chasse auditorium, while others headed inland to stay with friends or relatives.

Some nevertheless hunkered down to ride out the storm, despite mandatory evacuation orders.

“We’ve stayed for some pretty strong storms and we shouldn’t have,” admitted Keith Delahoussaye, a 60-year-old mechanic, at his trailer home in Port Sulphur.

He was keeping a close eye on the nearby Mississippi River.

“If we see the water rising here, we’ll leave,” he said.

In New Orleans, residents and business owners were laying down sandbags and boarding up windows while city officials set up shelters for residents.

But local revelers and tourists drank “hurricane” cocktails and sang arm in arm as they walked down Bourbon Street late Friday, ignoring warnings from Mayor LaToya Cantrell to stay indoors.

On Saturday, Cantrell again urged caution, saying: “A lot of the rain won’t happen until after landfall.” If the storm becomes a hurricane, it would be the first of the Atlantic season, which runs from June to November.

Louisiana is facing an extraordinarily dangerous confluence of conditions, experts say.

The level of the Mississippi River, already swollen from historic rains and flooding upstream, was at nearly 17 feet (5.2 meters) in New Orleans − just below flood stage.

River levels are expected to peak at just over 17 feet, according to Saturday’s forecast by the National Oceanic and Atmospheric Administration (NOAA).

But with storm surges of three to six feet projected, and 25 to 50 centimetres of rain forecast, authorities were keeping close watch on the 20-foot-high levee system protecting the city of 400,000.

“Much of the Gulf Coast, especially Louisiana, are already at extremely high water levels and so the heavy rains and any potential storm surge will lead to dangerous flash flooding,” Jill Trepanier, an expert at Louisiana State University, said in a statement.

Mike Yenni, president of Jefferson Parish near New Orleans, said the community had taken the “unprecedented” step of closing hundreds of flood gates, largely due to the high levels of the Mississippi.

Agence France-Presse