Emergency teams in the southern US are battling to reach survivors of Hurricane Katrina, the most destructive storm to hit the country in decades.
Hundreds of people are feared dead in Mississippi, and the Louisiana city of New Orleans is badly flooded.
The city mayor said rescuers were unable to retrieve the dead. "They're just pushing them aside," he said.
Amid worsening conditions, officials plan to evacuate a New Orleans stadium where up to 20,000 people took shelter.
The Superdome stadium is without power, and toilets are overflowing.
"It's a very, very desperate situation," Louisiana Governor Kathleen Blanco said.
One resident of New Orleans said escaping from the storm was "hell".
"We were screaming, hollering, flashing lights. It was complete chaos," Kioka Williams told the Associated Press news agency.
She had to hack her way through the ceiling of her beauty shop as flood waters rose in the city of half a million people - much of which lies below sea level.
Walls keeping water out of the bowl-shaped city have been breached, and emergency teams are using helicopters to drop 1,350kg (3,000lb) sandbags and concrete barriers into the gaps.
New Orleans mayor Ray Nagin said up to 80% of the city was submerged, in some cases by waters 6m (20ft) deep. He warned water levels could still rise.
"Some sections of the city which are dry now could see nine or 10 feet (some 3m) of water," he said.
The US Army Corps of Engineers says it could take a month to clear the flood waters, and the government's disaster relief agency has urged evacuees not to try to get back to their homes.
The BBC's Alastair Leithead in New Orleans says there is panic as vital supplies run out. Heavily armed police have been trying to impose a form of martial law to stem outbreaks of looting.
While some looters are stealing non-essential goods, others are simply trying to find food and water.
The situation appears to be even worse in Mississippi.
"You're going to be looking at hundreds dead along the coast," a state official said.
Casinos housed in barges have been hurled onto the beach and beyond. Tens of thousands are homeless, and officials say it could be weeks before power is restored.
"I can only imagine that this is what Hiroshima looked like 60 years ago," said Mississippi Governor Haley Barbour after viewing the destruction from the air.
Survivors are being found all the time, including two children who lost their parents.
Harrison County in Mississippi bore the brunt of Hurricane Katrina as it slammed into Biloxi and Gulfport before heading inland.
Mississippi media earlier reported 54 people killed in the state.
In Biloxi, 30 people were reported dead in one block of flats which was hit by a 9m (30ft) "storm surge".
The town's death toll may be "in the hundreds", municipal spokesman Vincent Creel said.
Louisiana's Governor Blanco urged residents to spend Wednesday in prayer and assured them the crisis would eventually be overcome.
The US Red Cross has mobilised thousands of volunteers for its biggest-ever natural disaster effort and federal emergency teams are being dispatched to affected areas.
President George W Bush, who has cut his holiday two days short, has called on Americans to donate to the Red Cross or other organisations.
Damage estimates of more than $25bn suggest it could be the US insurance industry's most expensive natural disaster ever.
The price of crude oil on the international market hit a record $70.85 a barrel due to the vulnerability of oil and gas fields in the Gulf of Mexico.
The US energy secretary has announced that oil will be released from government petroleum reserves.