President Obama has warned of serious flooding from Hurricane Isaac and says people should leave their homes if they are asked.
The president added that residents should listen to local authorities and follow their directions as Isaac approaches the Gulf Coast .
Speaking from the White House, the president said: "We are dealing with a big storm that could cause significant flooding and other damage.
"Now is not the time to tempt fate. Now is not the time to dismiss official warnings. You need to take this seriously.
"We have response teams and supplies, ready to help communities in the expected path of the storm. I want to encourage all residents of the Gulf Coast to listen to local officials and follow their directions, including if they tell you to evacuate."
With no compulsory evacuation plan, some New Orleans residents have to decide whether to stay or to go. Sky's Greg Milam spoke to one resident who could not face the thought of leaving.
"I thought it would be more traumatic for my family to leave," she said. "We watched the storm and determined it would not be as severe as anticipated, so we decided to hunker down.
"On Saturday I was getting preparations made and a lady and I were both reaching for - of all things - baked beans. Our eyes met and she just burst into tears; I did too.
"But we evacuated when Katrina came. I know people who lost everything. I have a friend who lost three brothers."
But thousands of residents outside the city's \$15bn flood protection system have already decided not to take their chances with Isaac and have made the decision to gather their belongings and flee.
"I'm gassing up and getting out," said Michael Lynch, a 52-year-old oil field worker, as he filled his truck's petrol tank. "I would have gotten out yesterday, but they said it wasn't going to be much."
Lynch intended to drive 130 miles (209 km) inland to Lafayette where he had family, and from where it would be easier to get to work after the Isaac passed.
New Orleans' main airport is now closed and buses and trains are no longer running, limiting evacuation options for residents without cars and for visiting tourists.
"We were supposed to fly out Wednesday, but that's not going to happen," said Kevin McCarthy, 54, who was visiting from New York. "For now, we're hoping to see some music and have a good time, then wait the storm out."
In a seperate televised address, the Governor of Florida, Rick Scott, said authorities were doing everything they could to help residents.
"Our concern right now is the panhandle," he said. "We have tropical storm gusts in the Pensacola area, this afternoon we'll have tropical storm winds through tonight.
"Our biggest concern is the Palm Beach area. They're pumping as much water as they've ever pumped in the history of the water management district."
Isaac has now been categorised as a hurricane as it makes its way towards New Orleans. It is expected to make landfall just a day ahead of the seventh anniversary of Hurricane Katrina, which devastated the area and killed 1,800 people.