Most of the hurricane survivors who volunteered to leave New Orleans have now gone from the city, officials say.
Between 5,000 and 10,000 people are believed to remain, despite the mayor's compulsory evacuation order.
Police officers have denied using force to clear the flooded city, but say they may start to do so.
Meanwhile, an opinion poll suggests that two-thirds of Americans think the president could have done more in the aftermath of Hurricane Katrina.
The Pew Research Center also found that two-thirds of the African-Americans asked believed the government reaction would have been faster if most of those affected had been white.
American political figures have criticised the slow response to the disaster.
Former Secretary of State Colin Powell has added his voice, in a TV interview to be broadcast in the US on Friday.
Mr Powell said he could not understand why more preparations had not been made.
But he said so many African-Americans were left unprotected because they were poor, rather than because they were black.
US Under-Secretary of State Karen Hughes said allegations that President Bush was not doing all he could to help were heartbreaking to him.
New Orleans Police Chief Eddie Compass told the Associated Press that a "sensitive" approach would be used to remove people.
KATRINA'S CONFIRMED DEAD
Mississippi - 201
Louisiana - 118
Florida - 11
Alabama - 2
Georgia - 2
"We are not going to be rough," he said. " We are going to use the minimum amount of force."
Some residents told the agency they had left under extreme pressure.
The evacuation has been ordered for health reasons. E.coli and other dangerous germs have been found in the polluted floodwaters.
Several deaths have already been attributed to infected wounds.
In other developments:
- Some 25,000 body bags are being sent to the city, with Mayor Ray Nagin saying he fears the death toll could climb to 10,000
- About 60% of the city is still flooded, according to the Army Corps of Engineers
- Water is being pumped out by 37 of the city's normal pumps along with 17 portable pumps
Floodwaters are dropping to reveal dead bodies, raw sewage, fuel and rusting vehicles, and more homes are becoming accessible to search and rescue teams.
On Thursday, Congress approved a bill providing $51.8bn (£28bn) for the relief effort, on top of $10bn granted last week.
The new funds will be used mainly to pay for search and rescue operations, drinking water and medical assistance, officials said.
Mr Bush warned Congress it should expect further emergency requests.
Speaking at the White House, Mr Bush announced that every family affected by Hurricane Katrina would receive the initial sum of $2,000 in aid.
He also declared Friday 16 September a national day of prayer and remembrance for the victims.