Tropical Storm Isaac continues to lash New Orleans with heavy rain despite being downgraded, as residents in cars and homes were stranded exactly seven years after Hurricane Katrina devastated the city.
In the swampy bayous of rural Louisiana, rescuers in boats tried to reach people stranded there.
In New Orleans, the newly-fortified levee system appeared to be holding, though power lines were downed and debris littered the 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.
Isaac has top sustained winds of 70mph, just below the hurricane threshold of 74mph. The storm is about 50 miles west-southwest of New Orleans, where it is bringing drenching rain and fierce winds.
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, he 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, a rural area south of New Orleans, 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.
Rescuers in boats and trucks plucked a handful of people who became stranded by floodwater in thinly populated areas of south-east 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.