many residents returning to Battery Park City at the end of last month found a leaflet from Tribeca Hardware under their doors, offering to order Holmes air monitors for their dust-filled rooms. But the store's owner, Paul Weisenfeld, could only be contacted by cell phone.

His popular shop on Chambers Street with its crammed shelves was located behind a chain-link security fence guarded by police and soldiers, which sealed off much of the area of lower Manhattan around the ruins of the World Trade Centre.

Recently, the barrier has been moved back slightly and Tribeca Hardware is open once more, but it has lost 25 days' trading and up to $100,000 (€110,000) in business. The same goes for hundreds of other small businesses in the area.

Some, like the popular Gee Whizz Diner, remain accessible only to rescue workers. Others, such as clothing shop Sorelle Firenze just outside the security zone, have seen their sales drop by 50 to 90 per cent, and are giving huge discounts and free gifts just to keep customers coming in.

But many of the customers have gone for good. Some 50,000 people worked in the seven towers of the World Trade Centre. Five thousand died on September 11th and the rest have been put out of work or displaced. Thousands more workers have also gone from adjoining, evacuated buildings such as the 32-storey glass and marble north tower in the World Financial Centre, where 9,000 traders, analysts and other staff at Merrill Lynch once occupied three million sq feet of space.

They are now toiling in overcrowded cubicles at offices in New Jersey and elsewhere. So many banking and brokerage firms have moved across the Hudson from south Manhattan that Jersey City has become known as Wall Street West. Local businesses in south Manhattan hope they will come back but a great number of displaced employees are not keen to return any time soon.

Incredibly, the rubble of the twin towers, extending 100 feet below ground in places, is still smoking like a volcano and producing an acrid smell; steel beams have been pulled from the depths still glowing red at one end. Ground Zero is a crime scene with $200 million worth of gold and silver buried in deep vaults and the security restrictions will not be lifted any time soon.

While a forest of tall cranes swing back and forth, police in white protective suits and masks pick through the debris for personal possessions and human remains. The tomb of twisted metal and rubble will never yield up most of the victims, however, such was the immense cumulative weight of the three foot-deep concrete floors collapsing one on top of another and pulverising everything below.

The resulting dust storm that exploded over southern Manhattan left a thick coat of dust on the abandoned computer terminals and telephones at the Wall Street Journal's offices in the World Financial Centre. Evacuated as the towers burned, the staff were transferred 50 miles away to South Brunswick, New Jersey.

When Peter Kann, chief executive of parent company Dow Jones, informed the newspaper's workers on Tuesday that 425 of 750 journalists and executives would return to Manhattan by the end of the year, many objected. Some are "frankly terrified of going back to the place" because of the possibility of asbestos particles exceeding safety levels, according to union representative Gardiner Harris.

On the other hand, some of those required to stay in South Brunswick face long commutes from homes in greater New York.

Other companies have not had to move as far. Employees of Lehman Brothers have occupied rooms in a Sheraton hotel uptown. The 1,200 traders of the New York Board of Trade once took up 12,000 sq feet at the now-wrecked number four World Trade Centre building - the location of the "pit" where Dan Aykroyd and Eddie Murphy bet on orange juice futures in the 1983 film Trading Places. They are now crowded into a quarter of the space in a warehouse in the borough of Queens, which with some foresight had been reserved as a back-up location after the 1993 Trade Centre bombing. They will remain there, trading coffee, cocoa and cotton, for several months until new Manhattan premises are found.

The 616 companies that occupied the World Trade Centre have similarly been scattered to neighbouring regions and states. Employees have been split up and in many cases analysts and bankers have to cope with slow internet speeds and lost telephone contacts in suburban offices or apartments.

Getting post is a major logistical dilemma for them and also for a postal service burdened since the attack with the anthrax scare. Some 90,000 letters and packages still arrive every day for addresses in the World Trade Centre that no longer exist, for people who are no longer living and for financial workers moved to far-off locations. The twin towers received so much mail that it had its own zip code - 10048.

Trade Centre delivery workers such as Emma Thornton, 57, who for three decades carried letters to the North Tower, now sort mail in a mid-town building in the hope the letters will be claimed. Bundles of post for the Windows on the World restaurant where 166 people died were only picked up last week.

Particularly heart-rending are the letters for individuals at Cantor Fitzgerald, the bond-trading firm that lost 733 of its 1,000 staff - but which is back in business in Darien, Connecticut. Some companies which closed, such as the Amish Market, a much-loved delicatessen and grocery store, have made it known they will not be reopening in the downtown area.

New York authorities claim 14,632 businesses in the area close to the World Trade Centre were destroyed, damaged or badly disrupted by the catastrophe, with losses running into billions of dollars. These range from the once-thriving Bangladeshi Taste of Tandoor restaurant at the corner of Church and Warren Streets, whose owners have had to lay off six of the eight staff, to paediatrician dentist Dr Renee Wild of Hudson Street - who says she has nobody to take care of any more.

Few of these enterprises had insurance to cover interruption of business and only 340 have so far got disaster relief loans from the Small Business Administration.

The only small business people doing good business, it seems, are the pedicab drivers who have abandoned the mid-town tourist areas to come and ferry brokers through streets in the financial district from which cars and taxis have been excluded.

Some of the traders who filled the narrow streets of lower Manhattan with the aroma of hot dogs, pretzels and roasted nuts have drifted back, but there are far fewer customers.

Frank Pastore, who had a lunch stall that was popular with the employees of the Board of Trade, was put out of business by the exodus and is not coming back. He found out where his clients had gone and took his cart all the way to Queens, where the coffee and orange juice traders are again lunching on his baked ziti in tomato sauce and submarine sandwiches.

See also pages 5 and 7