"In the next few months, we are likely to limit ourselves to only business travel. We would likely weigh the safety risks very carefully before we decide to fly again." That view is typical of many of the three million passengers who, on a normal day before Tuesday, would have taken a flight somewhere in the world. What will alarm the travel industry is that it is the opinion of one of the world's leading aviation safety experts, Dr Todd Curtis.

Dr Curtis heads the website, and has been working around the clock since the disaster to gather and assess information on the hijackings. At the same time, airline and tour operator executives have been meeting to try to predict the effects of the catastrophe on travel worldwide. In the short term, industry insiders believe passengers will react in the same way as they did to the Gulf War, but probably to a greater degree.

Travel companies are steeling themselves for a downturn in "discretionary" journeys – some business travellers will switch to video conferencing and other telecommunications solutions, while many leisure travellers are likely to defer journeys or simply decide not to fly at all. Rumours were circulating yesterday about possible airline failures in the event of a sustained fall in passenger numbers. Tour operators, who have invested heavily in aircraft and hotels, have seen a decline in the number of customers for late-availability holidays this month and next.

Yesterday's announcement of heightened security by Norman Mineta, the US Transportation Secretary, merely upgrades security at American airports to something approaching European standards. No longer will meeters, greeters or people with malicious motives be able to walk freely to any departure gate at any airport – only staff and ticketed passengers will be permitted. In the US and worldwide, air travel will become less easy and comfortable.

Dr Curtis fears that terrorists may now switch their attention to other means of transport. He warned yesterday that "modes of transport that involve many passengers and that have the potential for a lot of press coverage" are especially vulnerable. "Cruise ships are a possible target due to the potential for a very dramatic ending to a sabotage or hijacking incident."