Travellers at airports across the globe remained in limbo today following flight disruptions in the wake of the terrorist attacks at the World Trade Centre in New York and the Pentagon in Washington.

Hong Kong's airport authority said that 20 out of 30 flights to and from the United States and Canada had been cancelled on Friday, leaving more than 7,000 passengers stranded.

Airline officials said they had stepped up security with police, clad in blue uniforms and carrying submachine guns, patrolling the check-in areas for North American flights.

Australian air traffic was thrown into total chaos on Friday following both world events and the collapse of the nation's second largest airline, Ansett, just days after its parent, Air New Zealand, failed to find a buyer for the debt-laden carrier.

In Europe, Austrian Airlines said all flights to North America would remain grounded until Friday. Lufthansa said it had cancelled all 50 of its flights between Germany and the United States. It estimated that 16,000 passengers originally booked on its flights would be affected.

The German flag carrier added that it was uncertain whether it would fly to Canada on Friday, although the first five planes returning stranded passengers from Canada landed in Frankfurt overnight.

Czech state-run airline CSA cancelled its two scheduled flights to the United States on Friday due to continuing airspace restrictions. CSA had planned to resume flights to the United States on Friday, but the airline said it would not fly to or from New York's JFK Airport and Newark International Airport in New Jersey until the restrictions were lifted.