By Jonathan Duffy BBC News Online correspondent in New York

It has long been the number one destination for overseas visitors to the US. But since the attack on the World Trade Center, the Big Apple's tourism industry has gone rotten.

The Empire State Building, Central Park, the Guggenheim, shopping on Fifth Avenue, the Statue of Liberty, Radio City - New York has always been a tour guide's dream.

A British tourist hauls her luggage through New York's dusty streets

But these days the open-top sightseeing buses that sweep along Manhattan's grand avenues are eerily empty.

The Big Apple may be basking in a gloriously warm late summer, but since the World Trade Centre tragedy, tourists have been giving the city the cold shoulder.

Visitor numbers are down dramatically. Hotel occupancy rates have slumped from about 75% a fortnight ago to about 30% today.

Restaurant bookings are sharply down, as are museum attendances.

NY tourism industry

Valued at $25bn annually Employs 280,000 people 37.4m visitors came in 2000

Six Broadway shows are closing this week because of the precipitous slump in business, and tickets to shows like the Lion King, which had been like gold dust, are now readily available.

Already jobs have been affected. According to the Hotel Trades Council, 3,000 hotel workers have been laid off. That's about a tenth of those employed in the industry in New York City.

And no one knows when the trough will bottom out, or how deep it will be when it does.

No way home

For tourism, the effect of the terror strikes on the twin towers was both dramatic and instantaneous. Fearing further hijackings, the US government immediately sealed off its airspace.

Stranded tourists bedded down to wait for flights

Tourists bound for America were left stranded in airports around the world. Those already on holiday in the country had to sit tight and wait for flights to resume.

In Manhattan, the effect was even more pronounced. Three hotels in the vicinity of the trade center were evacuated and many of those hotels that did have vacancies offered rooms to the influx of rescue workers.

Despite the freeze on flights, business actually picked up at the New York's main walk-in Visitor Information Centre as visitors who had been due to return home sought advice on how to spend their extended stay in the city.

'Unique time to visit'

But since flights re-started, the steady stream of visitors arriving in the de facto capital, from abroad and elsewhere in the US, has thinned to a relative trickle.

Gareth and Elinor Lewis: On holiday from the UK

The nature of the terror attacks has put millions of people off air travel.

Gareth and Elinor Lewis, who arrived from London on Wednesday, said their flight was half empty. They had also thought about cancelling in the wake of what had happened.

"Initially we were worried. We thought that if Bush was going into a war we might be stranded over here," says Gareth, who is on a five-day break with his sister.

"Then we decided that now it was probably going to be more secure than ever to fly. And we also thought that this would be a unique time to be here because of what has happened."

City in mourning

Stepping out of the Metropolitan Museum of Art into unseasonably heavy rain, German tourist Sylvia Baumann says she is glad she came. But originally had it been up to her, she would have stayed away.

New Yorkers show their softer side

"I'm on a five-week trip and was in Boston last Tuesday when it happened. I wanted to go back to Canada but I couldn't change my flights."

She wasn't worried about flying so much as the atmosphere in New York.

"I didn't want to come because it was a bad feeling - a tourist in a city where thousands of people have just died."

It's that sort of attitude that is causing grave concern for Sunny Christopher, general manager of the Washington Square Hotel in Greenwich Village.

Occupancy in the hotel has never been below 50% in the 25 years he has worked there - until now. Although the nightly rate for a double room has been cut by more than a third, still only 30% to 40% of rooms are occupied.

Management is thinking about laying off staff at the 170-room hotel.

"When daily revenues drop from $30,000 or $40,000 to less than $5,000 you can't sustain all your employees," says Mr Christopher.

Shops are already selling souvenirs of the attacks

All this has come on the back of an already difficult year for the travel industry, with business travel being hit by the economic downturn.

Since the attack, several big conferences have been cancelled, including a two-week United Nations General Assembly that would have brought scores of statesmen and women to the city.

Three major trade shows have been called off at the Jacob Javits Center, which is currently doubling up as the hub for all disaster relief co-ordination.

New York's mayor, Rudolph Giuliani, whose credibility has soared with his handling of the crisis, has sought to add his magic touch by urging tourists to "come here to spend money".

Ticket sales for Broadway shows have been hard hit

New York's official tourism body, NYC & Co, is also trying to talk up confidence.

"The city is still very much open for business," declares spokeswoman Nell Barrett.

People will want to come and experience the support that has shown itself in past days

Nell Barrett

And she believes the unity that the tragedy helped forge among New Yorkers will make the city even more attractive to visitors in the future.

"People will want to come and experience the support that has shown itself in past days. I feel that we are like a village."

But, morbid though it may sound, the tourist value of what happened in lower Manhattan is already starting to reveal itself.

For days now the streets around "ground zero" - the scene of the devastation - have been buzzing with camera-wielding tourists.

Among sightseers, it seems, there is plenty of appetite for witnessing with their own eyes the fallout of the world's worst terror attack.