This exodus was even more desperate than the first.

As murky water surged around their homes from levee breaks undetected in the immediate aftermath of Hurricane Katrina, families that had hunkered down for Monday's storm were forced Tuesday to climb first to their attics and then to their roofs in the hope of rescue by boat or helicopter.

In the streets, cars filled with fleeing residents -- pet cages and luggage in tow -- stalled in chest-deep water. Scores of people could be seen trudging west on foot along deserted Interstate 10, lugging small packages of belongings, headed for refuge from the water that now covers 80 percent of this city.

"I have nothing but me, the children and what we have on our backs," said Molly Moses, a mother of five who was rescued from the roof of her two-story house four miles from the center of New Orleans. About daybreak, as the waters reached the attic, her fiance punched a hole in the roof, where she was found about 10 a.m. Tuesday clutching her 9-month-old daughter.

"We were just too busy trying to save our lives."

Rising floodwaters led to a second mass evacuation Tuesday from this low-lying metropolis of terrified residents who had avoided the storm's most direct destruction when it veered slightly to the east.

As the floods isolated even dry neighborhoods from authorities Tuesday, a sense of chaos enveloped much of the city. Looters smashed windows and dashed in unpursued. Smoke from two fires, apparently difficult for emergency crews to reach, rose on the horizon. Even the city's major daily newspaper had to bail out. Scores of employees of the Times-Picayune rushed out like refugees on the back of circulation trucks and wound up, after a long, sweaty ride, in Baton Rouge.

Hundreds of houses could be seen with water up to the eaves. Occasionally the tops of cars were visible, bobbing to the surface.

Fleets of speedboats, airboats and other water-going vessels were launched to patrol the inundated streets, searching for survivors. But the rescue teams were instructed to ignore bodies because there were no facilities to deal with them.

"Our main thrust is to get people out of the water. It's going to get up into the nineties today, and get oppressively hot," said W. Parke Moore III, an assistant secretary of the state Department of Wildlife and Fisheries, who is helping coordinate the effort. "They don't have sewage facilities or water to drink. We need to get them to a safe haven, and then the Louisiana National Guard will provide shelter."

After Hurricane Katrina passed Monday, many residents had been relieved to find their neighborhoods at least partially above water. But by late Monday, long after the rains had subsided, residents realized the floodwaters were still rising.

An emergency management flight Monday afternoon had discovered a break in one of the levees that protect this city from flooding, but its significance was not immediately known. On Tuesday, two levees were found to have been breached, and the saucer-shaped city was filling with water.

Cradled by Lake Pontchartrain and the Mississippi River, New Orleans sits below sea level. Under normal conditions, water levels are maintained several feet above the city. The intricate system of levees and pumps is supposed to prevent water from spilling over into city streets.

A break along the 17th Street Canal, which connects Lake Pontchartrain to the Mississippi River, is essentially allowing Lake Pontchartrain to empty into the city, and the levees are now holding water in. Several neighborhoods were submerged by as much as 10 feet. The French Quarter, one of the higher points in central downtown, was relatively dry Tuesday morning, however.

For thousands of residents, any attempt to repair the levees is already too late.

Hundreds of survivors were dropped off hourly at partially submerged St. Claude Bridge, a launching point for rescue boats. Many were weak from hunger and exhaustion and had to be helped, shaking, out of boats. Some carried laundry baskets full of clothes, others had food boxes, and a couple of children were clinging to teddy bears. For most, these were their last remaining possessions.

"When you watch the people get off the boats, their faces have an unforgettable expression -- they've been saved, but now what?" said Jim Sohr, who was standing on the bridge looking for signs of a friend who lived in one of the submerged homes.

A handful of people with missing relatives stood by the roadside, pleading with emergency workers to search places where their loved ones were stuck.

"I just want them to go and rescue my grandmother. She's on Delarus Street. She was on the roof. She's 65 and needs her insulin. We've been trying to get help, but they aren't going there. The rescuers just all seem to go in a circle," said Mike Jones, who was standing with two cousins. "They're senior citizens. They need help now."

Many of the residents left in New Orleans are poor, and while some people have criticized them for failing to heed mandatory evacuation orders, many residents say they were simply unable to get out for financial or medical reasons.

"People are saying that those stuck in New Orleans now are those that wanted to stay, but that's not true," said Danelle Fleming, a New Orleans-based social worker. "They wanted to leave, but they couldn't."

She said that the city's Greyhound station was closing Saturday afternoon -- even as people without cars were trying to leave.

After being rescued from her roof, Moses said she was among those unable to evacuate before the hurricane. "My mother-in-law went out of town, but I didn't have any money, so I couldn't," she said.

The only items she managed to hang on to were a bag of diapers for her daughter and a feeding bottle. She did not have time even to find her shoes.

Two of those belatedly heeding the instruction to evacuate were friends, Michael Thompson and Braden Clostil, who were walking west along deserted I-10 in search of Barnable High School, which they had heard was taking in the homeless.

"I had to sleep in water. I had no choice," said Thompson, 27, who works for a corporate housing company. "There were lots of rats and snakes which came from the canal and went everywhere, so you had to be careful about that."

Levees in New Orleans are designed to keep water several feet higher than the city, which rests below sea level. As levee walls have been breached, water is pooling in without an outlet. About 80 percent of the Crescent City is submerged.Evelyn Turner grieves for her companion, Xavier Bowie. The couple was unable to leave the city, and Bowie, who had lung cancer, died after his oxygen supply was depleted. Rescue crews took to the water and the air to find survivors.Police patrol for trespassers along Canal Street. Looting was reported in the city as a second mass evacuation was ordered. Many residents were able to carry only the essentials to nearby emergency shelters.