NEW ORLEANS, USA (AP) — Isaac's whistling winds lashed New Orleans and the storm dumped nearly a foot of rain on its desolate streets, but the system of levee pumps, walls and gates appeared to withstand one of the stiffest challenges yet. To the north and south, though, people had to be evacuated or rescued as Isaac lingered over Louisiana.

The rain fell almost constantly for more than a day, flooding neighbourhoods in a rural part of the state and in neighbouring Mississippi. Officials had to respond quickly because the waters were rising fast — even as Isaac meandered slowly northward today on a path toward neighbouring Arkansas.

President Barack Obama declared federal emergencies in Louisiana and Mississippi late yesterday, according to a statement from the White House. The disaster declarations free up federal aid for affected areas.

Along the shores of Lake Ponchartrain just north of New Orleans, officials sent scores of buses and dozens of high-water vehicles to help evacuate about 3,000 people as rising waters lapped against houses and left cars stranded. Floodwaters rose waist-high in some neighbourhoods, and the Louisiana National Guard was working with sheriff's deputies to rescue people stranded in their homes.

The floodwaters "were shockingly fast-rising, from what I understand from talking to people," Lt Gov Jay Dardenne said. "It caught everybody by surprise."

Isaac arrived seven years after Hurricane Katrina and passed slightly to the west of New Orleans, where the city's fortified levee system easily handled the assault. But, low-lying area outside the city were harder hit.

"Hurricane Isaac has reinforced for us once again just how vulnerable these critical areas are," Democratic US Sen Mary Landrieu said.

New Orleans' biggest problems seemed to be downed power lines, scattered tree limbs and minor flooding. One person was reported killed, compared with 1,800 deaths from Katrina in Louisiana and Mississippi. And police reported few problems with looting. New Orleans Mayor Mitch Landrieu ordered a dusk-to-dawn curfew.

But in Plaquemines Parish, a sparsely populated area south of the city that is outside the federal levee system, dozens of people were stranded in flooded coastal areas and had to be rescued. The storm pushed water over an 18-mile (29-kilometer) levee and put so much pressure on it that authorities planned to intentionally puncture the floodwall to relieve the strain.

Officials rushed to evacuate more than 100 nursing home residents from Plaquemines Parish, an area with a reputation for weathering storms and perhaps the hardest hit by Isaac. In this hardscrabble, mostly rural parish, even the sick and elderly are hardened storm veterans.

"I don't think we had to evacuate to begin with," said Romaine Dahl, 59, as he sat in a wheelchair. "The weather was a hell of a lot worse last night than it is now. And I got an idea that after all this is said and done they're going to say everything is over with, go on back home."

By early today, Isaac's maximum sustained winds had decreased to 45 mph (72 kph) and the National Hurricane Centre said it was expected to become a tropical depression by Thursday night, meaning its top sustained winds would drop below 39 mph (63 kph). The storm's centre was on track to cross Arkansas on Friday and southern Missouri on Friday night, spreading rain as it goes.

Forecasters expected Isaac to move farther inland over the next several days, dumping rain on drought-stricken states across the nation's midsection before finally breaking up over the weekend.

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