Nearly half of Louisiana is without power as Tropical Storm Isaac moved inland.

The Public Service Commission said 901,000 homes and businesses around the state — about 47 percent of all customers — are without power Thursday.

In Mississippi, utility companies said they are working to restore power to more than 150,000 customers in south and central parts of the state.

Isaac’s center bypassed New Orleans and its newly fortified levees as a hurricane Wednesday but flooded areas to the city’s north and south, where people had to be evacuated or rescued. It weakened slightly to a tropical storm but was still packing strong winds and torrential rain as it moves slowly across Louisiana.

The rain fell almost constantly for more than a day, flooding neighborhoods in Louisiana and Mississippi. Officials had to respond quickly because the waters were rising fast — even as Isaac meandered slowly northward Thursday on a path toward Arkansas.

President Barack Obama declared federal emergencies in Louisiana and Mississippi late Wednesday, allowing federal aid to be freed up for affected areas.

Along the shores of Lake Ponchartrain, officials sent scores of buses and dozens of high-water vehicles to help evacuate about 3,000 people as rising waters lapped against houses and left cars stranded. Floodwaters rose waist-high in some neighborhoods, and the Louisiana National Guard was working with sheriff’s deputies to rescue people stranded in their homes.

A tow truck driver was killed Thursday morning when a tree fell on his truck in Picayune, just across the state line from Louisiana in southwest Mississippi. Authorities said Isaac was causing heavy rain and strong winds at the time. They did not release the man’s name.

Even as Isaac weakened on its slow trek inland, it continued to spin off life-threatening weather including storm surges, inland flooding from torrential rain and potential tornadoes.

Early Thursday, a Coast Guard helicopter hoisted a couple and their dogs from a home in LaPlace, near the lake, after storm surge poured into their neighborhood and local authorities called for help. The couple was taken to New Orleans and reported in good condition.

The floodwaters “were shockingly fast-rising, from what I understand from talking to people,” Lt. Gov. Jay Dardenne said. “It caught everybody by surprise.”

Isaac arrived seven years after Hurricane Katrina and passed slightly to the west of New Orleans, where the city’s fortified levee system easily handled the assault.

Across the Mississippi Gulf Coast, signs of life began to return Thursday as curfews were lifted and some businesses and roads reopened, but many residents still couldn’t make it home because of flooding in low-lying areas and along rivers.

Bands of intermittent rain still pelted the soggy coast and there was gusting wind, but conditions had improved since the height of the storm.

Isaac was expected to dump heavy rain on much of central and south Mississippi on Thursday as the storm system meandered slowly northward Thursday on a path toward Arkansas.

Many roads remained impassable in some rural and low-lying areas. The Mississippi Department of Transportation reported some road closings due to downed trees and power lines.

Pearl River County Emergency Management Director Danny Manley said Interstate 59 in Pearl River County is covered by water 6 inches deep at its crossing over the Wolf River, and waters were rising just before 7 a.m. Thursday. Creeks in the county aren’t forecast to crest until early Friday morning, meaning flooding is likely to worsen throughout the day Thursday. County officials rescued four people from the waters overnight, Manley said.

He said high winds have also damaged some structures in the county, including ripping a roof off a mobile home in the Pine Grove community.

In Jackson County, rising waters were driving dozens of people from their homes in the Kreole community on the eastern edge of Moss Point.

There are also reports of high winds associated with a tornado warning in Pascagoula. City Councilman Frank Corder said at least two homes were damaged. There have been no reports of injuries.

New Orleans’ biggest problems seemed to be downed power lines, scattered tree limbs and minor flooding. One person was reported killed, compared with 1,800 deaths from Katrina in Louisiana and Mississippi. And few problems with looting were reported. New Orleans Mayor Mitch Landrieu ordered a dusk-to-dawn curfew.

But in Plaquemines Parish, a sparsely populated area south of the city that is outside the federal levee system, dozens of people were stranded in flooded coastal areas and had to be rescued. The storm pushed water over an 18-mile levee and put so much pressure on it that authorities planned to intentionally puncture the floodwall to relieve the strain.

Officials rushed to evacuate more than 100 nursing home residents from Plaquemines Parish, an area with a reputation for residents hunkering down to weather storms and perhaps the hardest hit by Isaac. In this hardscrabble, mostly rural parish, even the sick and elderly are hardened storm veterans.

By midafternoon Wednesday, Isaac had been downgraded to a tropical storm. The Louisiana National Guard ceased rescue operations in Plaquemines Parish, saying it felt confident it had gotten everyone out. There were no serious injuries. National Guard spokesman Capt. Lance Cagnolatti said guardsmen would stay in the area over the coming days.

By early Thursday, Isaac’s maximum sustained winds had decreased to 45 mph and the National Hurricane Center said it was expected to become a tropical depression by Thursday night, meaning its top sustained winds would drop below 39 mph. The storm’s center was on track to cross Arkansas on Friday and southern Missouri on Friday night, spreading rain as it goes.

Forecasters expected Isaac to move farther inland over the next several days, dumping rain on states across the nation’s midsection before breaking this weekend.