The usual welcome aboard is followed by a less familiar message as the intercom crackles into life on Delta Air Lines' flight 695 from New York to Atlanta, Georgia.

"Ladies and gentlemen," says the captain, "I would just like to tell you that every safety check has been done three times over, and that we wouldn't be flying today if your safety and security weren't assured."

Perhaps it comes as some small comfort to passengers. But most are too worried about safety even to have turned up at the airport: the rows of empty seats aboard the Boeing 737-800 are interrupted only here and there by any human presence.

It is a similar story aboard Trans World Airlines' flight 6090 from Atlanta to St Louis, Missouri, except this time, there are so few passengers aboard the McDonnell Douglas MD80 that the airline upgrades them all to the tiny first class section, leaving the 168-seat economy class cabin empty.

In the past week or so there have been plenty of statistics about the difficulties of the US travel industry following the hijackings and terrorist attacks on September 11, but they hardly convey the eerieness of the empty aircraft, deserted hotels and rows of vehicles in car rental lots.

At the airports, it is as though it is permanently 2am. The hubbub and the frenzy, the long lines at check-in desks and the jostling crowds around baggage carousels have gone, replaced by the sort of calm usually seen only in the small hours of the morning.

An agent at the Alamo car rental desk at Hartsfield Atlanta International Airport says business has gone through the floor. "Usually we rent 800 to 900 cars a day. Now it's down to 200."

The Hyatt Regency St Louis normally heaves with business travellers, convention visitors and tourists, but on one evening there are only two customers in the cavernous bar, and the next day all but 15 per cent of the rooms are empty.

Meanwhile, at a Starbucks cafe in Lambert-St Louis International Airport, staff have just learned that half the 30 jobs at the airport's six Starbucks outlets are to be cut because business is so slow. "I'm still trying to find out if I have a job tomorrow," says one employee.

In some ways, travelling has never been so easy. People can have their choice of aircraft seats and hotel rooms, and low demand means prices are tumbling.

Against that is the obvious anxiety provoked by the fact that the terrorists who carried out the attacks in the US used ordinary passenger airliners as their weapons, killing hundreds of travellers in addition to the people in the buildings that were hit.

US airport security, once lax by international standards, is now tighter. All kinds of knives, including plastic ones, are confiscated at the security gate, along with screwdrivers, nail clippers, tweezers and knitting needles. An off-duty Delta flight attendant had his American flag taken away because it was attached to a stick.

Even so, security is disconcertingly haphazard, with wide variations in regimes between one airport and another.

At the larger airports, such as those in New York and Atlanta, security personnel carry out random inspections of baggage, emptying out some passengers' carefully packed belongings and examining them in front of an audience of passers-by before roughly re-packing them. At St Louis, they use an X-ray scanner.

Yet at smaller airports, such as the one in Boise, Idaho, checked-in baggage is not examined and the only noticeable change in security is the appearance of a sign at the departure gate saying "no knives beyond this point".

At all airports, passengers' carry-on bags are scanned by X-ray machines, and passengers have to pass through metal detectors. But people are not normally frisked, so they could easily carry aboard weapons made of glass, plastic, ceramics or advanced composites. One paradox of the increased airport security is that it has become feasible only because passenger numbers have fallen so heavily. When numbers pick up again, the system could be overwhelmed unless it is reinforced or improved.

Hoteliers believe that pick-up could come quite quickly. The biggest reason for the slowdown, they say, is the cancellation of business meetings and conferences. Devon Sullivan, rooms division manager at the Hyatt Regency St Louis, says com-panies are "mainly cancelling to reschedule later down the road", as soon as business gets back to normal.

Still, travel was already declining before the terrorist attacks, and the mood among people still flying suggests hopes of any immediate uptick could be misplaced.

David Jones, a holiday-maker returning from St Louis to Cleveland, Ohio, still feels comfortable about flying. "It's much less crowded, and the chances of having a terrorist on the plane are pretty remote with all this security in place."

But Michele Younger, a sleep researcher en route from St Louis to a meeting in Denver, Colorado, says she feels very uneasy and would not be flying if she did not have to. "Why put yourself in a position where you're taking that chance?" she asks.

And Gail Slane, travelling from Denver to Boise, says she is flying only because she is going home after a holiday that she started before the attacks. "I won't be flying again for a very long time," she says.