Major storm Barry made landfall on the Louisiana coast on Saturday, slamming the region with heavy rains and ferocious winds as millions of Americans braced for the serious flooding expected to follow.

After briefly becoming the first hurricane of the Atlantic season, Barry was quickly downgraded to a tropical storm as it moved inland -- but it nevertheless packed a serious punch.

Authorities ramped up evacuations, airlines cancelled flights and flood gates slammed shut as the National Hurricane Center forecast the strengthening storm would reach hurricane status Saturday and roar ashore along the state’s central coast.

Tiffany Delee tosses a filled sandbag into the back of the family truck in Morgan City, Louisiana, on Friday.

The large storm system currently in the Gulf of Mexico brings heavy rains and potential storm surge and flooding that pose a threat reminiscent of 2005’s deadly Hurricane Katrina.

Thousands packed up and left their homes as flooding hit low-lying areas like Plaquemines Parish, where road closures left some communities isolated as they braced for Barry’s arrival.

By late Friday the storm was packing winds of 65 miles (100 kilometers) per hour, nine mph shy of hurricane strength.

Dozens took shelter in Plaquemines’s Belle Chasse auditorium, while others headed inland to stay with friends or relatives and avoid what the NHC called “life-threatening flooding” to coastal and river areas.

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

“No one should take this storm lightly, and I urge everyone to remain informed,” Edwards said on Twitter.

If the storm becomes a hurricane, it would be the first of the Atlantic season, which runs from June to November.

With Barry threatening massive rainfall across several states including Louisiana, Mississippi, Alabama, Arkansas and Tennessee, states of emergency were being declared to help free up federal resources to address the storm.

“We could be looking at widespread major flooding across several river basins,” the NHC said.

Some Plaquemines residents were battening down to ride out the storm, despite mandatory evacuation orders.

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

But he was keeping a close eye on the level of the Mississippi River nearby. “If we see the water rising here, we’ll leave.”

Donald Brown, operations manager for Plaquemines Medical Center, said most people had evacuated.

“I’d say they fear it every time,” said Brown, 58, who survived Katrina and was staying behind to look after the medical centre. He said “it would be devastating” if the river breached the levee.

Agence France-Presse