I think with every day, every hour and every minute that goes by, that hope diminishes. Right now it's not looking too good

Bernard Kerik New York police chief

Recovery workers have retrieved just 218 bodies from the wreckage of the twin towers, in which over 5,000 people are missing and increasingly presumed dead.

For a week, local leaders have kept hope alive that people could have been trapped within air pockets after the building collapsed.

New York is struggling to return to normal

There had been great anticipation that people trapped in the seven basement storeys of the World Trade Center - once shops and car parks - might have survived.

"I think with every day, every hour and every minute that goes by, that hope diminishes. Right now it's not looking too good," said Commissioner Kerik.

"The heat at the lower levels is very extreme and it's really taken a toll on firemen finding survivors down there," he said.

Such conditions, said Commissioner Keri, rendered the chances of finding survivors "very slim".

His comments could only add to the gloomy prospects already laid out by New York mayor Rudolph Giuliani on Tuesday.

"We don't have any substantial amount of hope that we can offer to anyone that we're going to be able to find anyone alive," said the mayor.

"We have to prepare people for the overwhelming reality that the chance of recovering anyone alive is very, very small."

Unstable foundations

Meanwhile the operation itself grows increasingly perilous.

Engineers are worried about small amounts of water starting to trickle into what remains of the metro station beneath the World Trade Center.

Relatives do not know whether to keep hoping

They are afraid that if the foundations of the building collapse, large volumes of water from the Hudson River just across the street will flood the site and then pour into the main subway system.

Contractors are planning to block any flow by inserting giant concrete plugs into the ends of the tunnels beneath the WTC.

But determined workers press ahead with the task.

On Wednesday they retrieved the bodies of two colleagues, two policeman who figured among the many emergency workers who were caught in the collapsing building as they assisted with evacuation.

No-one has been pulled out alive since last Wednesday, a day after the attack.

This is the end of my journey, now we have to wait for detectives to call us, now we wait and pray

Victim's brother Robert Dorf

Some 50,000 tonnes of rubble have been removed, but this is just a fraction of what needs to be shifted.

The total number of missing currently stands at 5,422, with just 152 out of the 218 bodies recovered identified.

Posters of missing people are plastered around New York, and makeshift memorials have sprung up in front of police and fire stations.

In the overwhelming atmosphere of despondency, people seeking their missing loved ones do not know whether to give up hope.

Some have provided DNA samples in a last-ditch attempt to find out what happened to them.

"This is the end of my journey, now we have to wait for detectives to call us, now we wait and pray," said Robert Dorf, whose brother Stephen was on the 84th floor of the Center's south tower.

Jennifer Liang, wife of fireman Kevin Bracken who was buried under the north tower when it collapsed, has accepted that her husband will never come back.

But she also realises that colleagues still searching for him need to have hope that he is alive.

"It's difficult for me when they say that perhaps they'll find him," she said.

"They are there all the time, risking their own lives in holes in the rubble and they need to believe that there is still hope."