New Orleans residents should consider delaying their return, the head of the Hurricane Katrina recovery effort has said - contradicting the city's mayor.
Some have returned to try to salvage homes and businesses
Vice Adm Thad Allen said the mayor's plans to get people back to their homes were "extremely problematic."
Mayor Ray Nagin wants to let 200,000 people back in the next 10 days.
But Adm Allen said services such as water, sewage, electricity and health care were not yet capable of supporting a large influx of people.
"I urge all residents to use extreme caution if they return and to consider delaying their return until safer and more liveable conditions are established," he said in a statement.
Mayor Nagin has called on business owners to return to help get New Orleans back on its feet, nearly three weeks after Hurricane Katrina left 80% of the city under water.
About 40% of the Louisiana city is still flooded.
The BBC's Claire Marshall in New Orleans says the displaced victims will be unsure which advice to follow.
Some of those who have started to trickle back have said there is no custom for their enterprises.
"Everyone is anxious to come back and see if their place is OK," Kevin Molony, who runs a company conducting tours of the city, told AFP agency.
"It's a ghost town. Tourism has been slammed."
Armed police and troops are continuing to patrol the streets in an effort to maintain security and prevent looting. A night time curfew remains in force.
In his weekly radio address on Saturday, President George Bush said the federal government would assume the bulk of the costs for "one of the largest reconstruction efforts the world has ever seen".
Restaurateurs have set up makeshift kitchens to prepare food
Congress has already approved $62bn for the recovery effort along the Gulf Coast, but that is expected to run out next month.
Mr Bush has indicated that the recovery programme, which White House officials say could cost up to $200bn (£110bn), might be partially funded by spending cuts in other areas.
He has ruled out raising taxes.
The president's approval ratings have slumped to 40%, the lowest of his time in office.