Nobody knows why about 30 elderly residents were left to die in the rising floodwaters, but the signs of their final, terrified struggle to survive can be seen in every mud-smeared room and corridor.

Over the front window, a table nailed to a window and wedged in place by an electric wheelchair shows that some desperate soul tried in vain to keep the storm at bay.

Stretchers at the front door — which now opens out on a 4ft-deep moat of reeking floodwater mixed with oil and sewage — bear witness to an abortive rescue mission launched by neighbours as the waters rose more than 6ft in less than half an hour. Some of the luckier residents were floated out on mattresses.

Inside, a foot of filth covers everything and clouds of mosquitoes swarm around. The chaos of those last hours is evident: an axe on the reception desk, mattresses all over the floors, hammers and nails next to hastily boarded windows. Electric wheelchairs lock wheels with trolleys while outside in the mire, where the floodwaters have now receded, car roofs are matted with mud and foliage.

The private nursing home was once a neat complex of aluminium-sided buildings that was supposed to be a haven of safety, standing in woods on the edge of the suburb of Chalmette, 20 miles southeast of New Orleans across the Mississippi River. But it was apparently abandoned by the five nurses who had originally opted to stay behind to care for their charges during Hurricane Katrina.

Cut off from the outside world, it kept its grim secret for more than a week after the hurricane hit. Then, on Tuesday, “disaster mortuary” teams arrived by boat to remove the corpses from the home.

Jack Stevens, the St Bernard Parish sheriff, said “30-plus” bodies — about half the home’s residents — were found inside. At least one elderly resident was reportedly found lying in thick mud on the floor, wrapped in a shower curtain. The corpse of another elderly woman was draped across her wheelchair.

The coroner, Bryan Bertucci, said the bodies were taken to a nearby hospital for identification. Those that did not have patient ID tags on them would be identified using DNA or dental records. He said it had not yet been established whether the bodies included care workers or Mabel Mangano, the owner of the home, who has not been traced.

He said he had offered Ms Mangano two buses at 2pm the day before Katrina hit to evacuate her residents. Ms Mangano declined, believing many of her charges, some of whom were in their 80s or 90s, were too frail to be moved. “She said, ‘I have five nurses and a generator and we’re going to stay’,” he said. “I think she made a poor decision.” Mr Bertucci he did not know where Ms Mangano, the nurses or their families, who had moved in for the storm, had ended up in the chaos of the evacuation.

“I think (the residents) probably died in their beds. If they could stand up they may have survived but we’re talking 60, 70, 80-year-old people. Just the stress may have been enough to kill them.” Nita Hutter, a Louisiana state legislator, said that staff left residents behind.

In New Orleans yesterday rescue teams began pulling bodies from the receding floodwaters, and the Federal Emergency Management Agency brought in 25,000 body bags. Eleven days after the hurricane, the suburban houses and streets of Chalmette were still covered in glistening black mud, cars thrown on to collapsed garage roofs, roads blocked by water and fallen trees.

Oil workers tried to pump thick sludge from a ruptured refinery from the town’s canal and the squashed remains of an alligator were smeared across the road alongside dead catfish. No residents were to be seen.

The total death count is expected to reach as many as 10,000. There were reports of up to 25 bodies washed into a ditch in a nearby town and of more than 100 people dying at a dockside warehouse while waiting for rescuers. Mobile mortuary units have been set up in the city to process the increasing tide of bodies, many unrecognisable after more than a week in the water.

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