Up to 40 aircraft are operating round-the-clock to move thousands who had
been stranded in New Orleans.
On Saturday President Bush announced the deployment of thousands of extra troops in affected areas, amid criticism of the rescue effort.
Survivors have been telling harrowing tales of violence.
On Saturday more than 10,000 people were removed from flood-ravaged New Orleans.
After spending days without food, water or medicines among rubbish and human waste, survivors appeared numb as they stumbled towards buses and helicopters.
Map of central New Orleans
The exact number of victims is still unknown, but thousands are believed to
have died.
People who died while waiting to be rescued could be found among the survivors just outside the convention centre.
There is no humanly possible way of knowing at this stage how many people like that still exist in this vast urban area
Michael Brown
Head of emergency operations
Many survivors have witnessed scenes of violence, including rapes and murders at the shelters, mainly carried out by criminal gangs.
"There is rapes going on here," Africa Brumfield, 32, who was staying at the convention centre, told Reuters news agency.
"Women cannot go to the bathroom without men. They are raping them and slitting their throats," she said.
A National Guard soldier described a similar incident. "We found a young
girl raped and killed in the bathroom [at the arena]," he said.
"Then the crowd got the man and they beat him to death."
The vast majority of those stranded were poor black people who may not have had the means to leave New Orleans ahead of Hurricane Katrina.
On Saturday, in a televised address from the White House, Mr Bush acknowledged the response had been too insufficient and spoke of an "incalculable" human cost.
"The magnitude of responding to a crisis over a disaster area that is larger than the size of Great Britain has created tremendous problems that have strained state and local capabilities," he said.
"The result is that many of our citizens simply are not getting the help they need, especially in New Orleans. And that is unacceptable."
More than one million people are said to be displaced. Most of them are in Texas, Tennessee, Indiana and Arkansas.
The president has signed off a $10.5bn (£5.7bn) emergency spending package approved by Congress.
The head of the Federal Emergency Management Agency (Fema), Michael Brown, said countless people across the city still needed to be rescued.
"There is no humanly possible way of knowing at this stage how many people like that still exist in this vast urban area," he said.
Mr Brown said relief workers had opened a mortuary and were collecting corpses,
many of which have been floating down flooded streets.
