NEW ORLEANS, USA (AP) — Tropical Storm Isaac continued to lash New Orleans with heavy rains today even as it was downgraded to a tropical storm.

A newly fortified levee system appeared to be holding exactly seven years after Hurricane Katrina devastated the city. In a drenched part of rural Louisiana, rescuers on boats snatched dozens of people stranded by floodwaters.

In New Orleans, power lines were downed and debris littered streets, prompting officials to impose a dusk-to-dawn curfew. Louisiana officials said they may have to intentionally breach a levee in a flooded area as Isaac made a slow, drenching slog inland from the Gulf of Mexico.

In a hard-hit rural area southeast of New Orleans, officials rescued dozens of people by boat, while authorities feared more in Plaquemines Parish could need help after a night of slashing rain and fierce winds that knocked out power to more than 700,000 households.

Isaac has top sustained winds of 70 mph (112kph), just below the hurricane threshold of 74 mph (119kph).

Louisiana Governor Bobby Jindal said officials may cut a hole in a levee on the east bank of Plaquemines Parish to relieve pressure on the structure. At a news conference in Baton Rouge, Jindal said there was no estimate on when that might occur. He said as many as 40 people are reportedly in need of rescue in the area.

Plaquemines Parish has also ordered a mandatory evacuation for the west bank of the Mississippi River below Belle Chasse, worried about a storm surge. The order affects about 3,000 people in the area, including a nursing home with 112 residents. Officials said the evacuation was ordered out of concern that more storm surge from Isaac would be pushed into the area and levees might be overtopped.

The hurricane also canceled commemoration ceremonies today for Katrina's 1,800 dead in Louisiana and Mississippi. Isaac was testing a New Orleans levee system bolstered by US$14 billion in federal repairs and improvements after the catastrophic failures during Katrina.

Army Corps spokeswoman Rachel Rodi said the city's bigger, stronger levees were withstanding the assault.

"The system is performing as intended, as we expected," she said. "We don't see any issues with the hurricane system at this point."

New Orleans Mayor Mitch Landrieu issued a curfew for the city as Isaac lashed the city on the seven-year anniversary of Katrina's destructive arrival.

Police cars had been patrolling the nearly empty streets since Isaac began bringing fierce winds and heavy rains to the city Tuesday night. The curfew was set to start tonight and would last until further notice.

Rescuers in boats and trucks plucked a handful of people who became stranded by floodwaters in thinly populated areas of southeast Louisiana. Authorities feared many more could need help after a night of slashing rain and fierce winds that knocked out power to more than 600,000 households and businesses.

The storm drew massive attention because of its timing —coinciding not only with the Katrina anniversary, but also the first major speeches of the Republican National Convention in Tampa, Florida.

Isaac also posed political challenges with echoes of those that followed Katrina, a reminder of how the storm became a symbol of government ineptitude.

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