Hurricane Isaac was downgraded Wednesday afternoon to a tropical storm but continued to hover over Louisiana with heavy rains and damaging winds. The storm, which was a Category 1 hurricane for 24 hours, has since sustained weakened winds of 75 mph, the National Hurricane Center reported. The storm's latest recorded location was about 50 miles west-southwest of New Orleans, moving to the northwest at 6 mph.

Isaac has knocked out power to more than 725,000 customers in five states as of Wednesday afternoon, the affected utilities reported. WWLTV in New Orleans reports that the CEO of Entergy Louisiana said power could be out for nearly half of the region's customers for at least a week after the wind and rain plowed through the company's energy grid.

New Orleans Mayor Mitch Landrieu issued a curfew for the city, set to start Wednesday night and last until further notice.

Hurricane Isaac's progress, which was stalling over southern Louisiana Wednesday, is expected to cause as much as $1.5 billion in insured losses, according to CNNMoney.

On a more positive note, the multibillion-dollar barriers built to protect the city of New Orleans after the 2005 Katrina disaster have not been breached, officials said.

"The federal levee system is fine," Landrieu told local radio.

"There are no risks. It is holding exactly as we expected it to and is performing exactly as it should. There are no people on rooftops from flooding that even approximates what happened during Katrina," Landrieu said.

President Barack Obama received a briefing from federal emergency officials on the impact of Isaac and held a conference call Wednesday with the governors of Louisiana, Mississippi and Alabama, and the mayor of New Orleans, the White House said.

"The president heard from the governors and mayor about the current conditions on the ground and the steps their teams are taking to respond. The president asked the governors to continue to identify any additional needs if they arise as the effects of Isaac and the response efforts continue," the White House said.

According to a Reuters report, police and National Guard units wielded automatic assault rifles as they monitored the streets of New Orleans amidst the hurricane that forced many residents and tourists into hiding.

"Thus far it's been pretty easy," Capt. Jeremy Falanga of the Louisiana National Guard told Reuters. "Not many people are outside; it's pretty buttoned up."

Around 4 a.m. on Wednesday, Plaquemines Parish Emergency Management and local law enforcement officials reported significant flooding from overtopping of levees in the East Bank portion of Plaquemines Parish, an area south of New Orleans.

The hours after the surge saw flash flood warnings for several Louisiana towns, including Timberlane, Metairie, Marrero, Kenner, Harvey, Avondale, New Orleans, New Orleans East, Chalmette and Hahnville. The warnings, which affect St. Bernard, St. Charles, Orleans and Jefferson parishes, are in effect until 9:45 a.m. CDT Thursday.