NATIONAL NEWS (CNN) — National Guard troops were working early Thursday to evacuate thousands of people west of New Orleans after a storm surge brought on by hurricane-turned-tropical storm Isaac forced water over the banks of Lake Pontchartrain.
Dozens of buses were being used to move residents out of flooded portions of St. John Parish, while authorities worked to rescue others trapped by up to six feet of water.
"We're continuing to rescue people from different areas throughout the parish," said Paige Falgoust, communications director for St. John the Baptist Parish.
"Our main focus right now is getting people out of their homes."
By nightfall Wednesday, about 1,500 people were evacuated, and another 1,500 were expected to leave their homes, Gov. Bobby Jindal's office said.
President Barack Obama signed major disaster declarations for Louisiana and Mississippi after slow-moving Isaac pummeled the Gulf Coast, dropping more than 20 inches in some locations and creating a dangerous storm surge.
Some 840,000 people in Louisiana, Mississippi, Arkansas, Texas and Alabama were without power, and water boiling advisories were being issued in a number of towns and cities along the Gulf Coast.
Airports from Baton Rogue to Biloxi were closed until at least Thursday as the stubbornly, slow moving storm continued to saturate the region.
Isaac made landfall as a Category 1 hurricane, seven years to the day Hurricane Katrina swept ashore in Louisiana and Mississippi. Katrina killed 1,800 people, most in New Orleans after the levee system failed and the city flooded.
Isaac's greatest punch bypassed New Orleans, taking aim at surrounding communities.
The storm was just south of Baton Rogue early Thursday, moving at about 6 mph with maximum sustained winds of 60 mph, the National Weather Service said.
Dusk-to-dawn curfews were in effect from New Orleans to Baton Rouge, where authorities were urging residents to stay inside and ride out the slow moving storm.
The situation was particularly dire in Plaquemines Parish, southeast of New Orleans, where 3,000 people remained in one area close to an 8-foot tall levee that waters are threatening, Jindal's office said.
An initial estimate by local parish officials showed as many as 800 homes may have received significant water damage, Jindal said earlier.
The U.S. Army Corps of Engineers reported significant storm surge in the parish, scene of many rescues. One involved National Guard troops who moved 112 residents from the Riverbend nursing home to another facility.
Dozens of Louisiana families that had ignored mandatory evacuation orders in a low-lying area retreated to their attics and roofs and sought rescue amid the howling wind and pounding rain.
Officials were considering intentionally breaching the levee downstream to allow some of the floodwater to flow back out of the inundated area, Jindal said.
That could happen as early as Saturday, said Billy Nungesser, the parish president. A report, though, in The Times-Picayune said digging could begin as early as Thursday.
"We are still looking for stranded residents," Nungesser said Wednesday night.
"We will resume a double check tomorrow on the homes on the east bank (of the Mississippi River). We're checking the west bank for anyone who may have been trapped."
While New Orleans reported relatively minor damage from the storm, officials said there were at least 12 incidents of looting in the city. New Orleans Police said arrests were made in each case, but didn't specify how many people were involved or where the arrests occurred.
In Mississippi, Gov. Phil Bryant said Wednesday that 34 people were rescued by boat in Hancock County, on the coast northeast of New Orleans, and 15 others were picked up by National Guard troops in trucks.
St. John Parish was virtually cut off Wednesday after Isaac's torrential rain and storm surge made nearly all roads in and out impassable, she said.
Parish officials were cross-matching records to make sure no residents were overlooked in the haste to get people out, Falgoust said.
The parish, with a population of about 32,000, was spared Katrina's devastation.
This time it wasn't so lucky.
The storm surge from Lake Ponchartrain came quickly and "in a different way from what we were expecting," Falgoust said.
The surge was unusually bad in LaPlace, about 25 miles northwest of New Orleans, where many people had been rescued or still needed to escape rapidly rising water.
"We have established pickup points in certain subdivisions that are easy access for our residents to get to by foot," she said.
People were being taken to a processing center at a church then bused to state shelters outside the parish.
"In some areas the water levels rose in 10 minutes to where they could not get out of their homes," she said.
CNN's Brian Todd, Soledad O'Brien, Ed Lavandera, Martin Savidge, John Zarrella, Chandler Friedman, Anika Chin, Mike Ahlers, Aaron Cooper and Ed Payne contributed to this report.