Authorities warned people in a handful of towns outside of New Orleans to get out early Thursday ahead of rising water brought on by hurricane-turned-tropical storm Isaac, which dumped more than 20 inches of rain in some areas.
The warning came as the storm claimed its first fatality. A tow truck driver attempting to clear debris on a road in Mississippi was struck by a falling tree, officials said. The incident took place at midnight, said Amanda Harris, deputy director of the Pearl River County Emergency Management office.
The National Weather Service said it received reports of the fatality in Picayune, Mississippi.
On Louisiana's border with Mississippi, residents of Washington Parish were alerted that the Bogue Chitto River was expected to rise by 14 feet overnight.
To the southwest, in St. John Parish, National Guard troops looked for people stranded after thousands were forced to flee when a surge forced water over the banks of Lake Pontchartrain.
"What we're doing is we have got law enforcement and fire personnel who are going door-to-door to notify people," Tommy Thiebaud, the Washington Parish director of emergency services, told CNN early Thursday.
Meanwhile in Plaquemines Parish, southeast of New Orleans, 3,000 people remained in an area close to an 8-foot tall levee that waters were threatening, Gov. Bobby Jindal's office said.
About 100 people who had ignored an evacuation order were rescued Wednesday in a flooded part of the parish, officials said. On Thursday, authorities from the sheriff's office and National Guard "will begin looking house to house to make sure they got everyone," said Parish President Billy Nungesser.
"We didn't have time to panic," Rafael Delgadillo of Braithwaite, Louisiana, told CNN Thursday. He, his wife and daughter were rescued by a neighbor Wednesday. "We were in survivor mode," he said.
Nearly a million customers were without electricity across Arkansas, Alabama, Louisiana, and Mississippi. Utility companies reported more than 978,000 customers without power.
Water boiling advisories were being issued in a number of towns and cities along the Gulf Coast.
Isaac was centered 55 miles southeast of Alexandria, Louisiana, early Thursday, moving slowly at about 8 mph with maximum sustained winds of 45 mph, the National Weather Service said.
A flash flood emergency was issued for Slidell, Louisiana, until 9 a.m. CT (10 a.m. ET). Surge flooding from Bayou Bonfouca and the W-14 canal gushed into parts of the city, and sudden inundation of up to five feet was possible in low-lying areas, the National Weather Service said.
Evacuations were under way in the city Thursday morning.
Authorities expected some street flooding in a few subdivisions on the south side of town, "but at present, that street flooding is minimal," the city said in a statement Thursday morning.
At Mississippi's Lake Tangipahoa, a dam is "expected to fail," the National Weather Service said, issuing a flash flood warning until 11:15 a.m. CT. Water levels could reach 8 feet, the service said.
If that happens, pastures and woodlands, along with some crops near the river, would be inundated, and parts of a highway would become impassable, forecasters said.
Throughout parts of the Gulf Coast, the National Weather Service warned, "life threatening hazards from storm surge and inland flooding are still occurring."
Issac is believed to have spawned three tornadoes overnight in Mississippi and Alabama, the weather service said.
Tornadoes are suspected to be behind damage in Gulfport and Jackson, Mississippi, while a twister is blamed for knocking down power lines and damaging a home in Geneva, Alabama.
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.
Isaac made landfall as a Category 1 hurricane seven years after Hurricane Katrina swept ashore in Louisiana and Mississippi. Katrina is blamed for the deaths of 1,800 people, most in New Orleans after the levee system failed and the city flooded.
Isaac's greatest punch bypassed New Orleans.
The city reported relatively minor damage from the storm, and officials said there were at least a dozen incidents of looting. New Orleans Police said arrests were made in each case, but didn't specify how many people were involved or where the arrests occurred.
Still, New Orleans will continue to face some pounding rain on Thursday, forecasters say.
"This storm took forever to get here, and now it doesn't want to leave," said Lt. Col. Jerry Sneed, deputy mayor in charge of public safety.
National Guard troops and authorities searched St. John the Baptist Parish for people trapped by up to six feet of water.
By late Wednesday, about 1,500 people were evacuated from the parish, and another 1,500 were expected to leave their homes, Jindal's office said.