Dublin, Cork and Shannon airports will be on heightened security alert today following the attacks in the US, according to Aer Rianta.
People booked on transatlantic flights were advised not to come to the airports today because journeys scheduled to the US had been cancelled.
A spokeswoman for Aer Rianta said Aer Lingus, Delta and Continental airlines, which fly from the Republic to destinations across the US, have cancelled their flights until further notice.
Last night, the British Prime Minister, Mr Tony Blair, warned he would not allow flights over central London.
A spokesman for Aer Rianta said this would create delays for flights leaving Ireland as a result of air traffic control changes.
It is not yet known when transatlantic flights will resume or when passengers stranded in the US will be able to return to Ireland.
Travel agents were predicting yesterday there would be no flights to or from the US for at least a number of days.
Aer Lingus has set up an information line for people who have transatlantic bookings. The number is 1800 222221. For those in the US, the number is 1866-IRISH- FLT.
Delta's 24-hour reservation line is 1800 768080 and Continental can be contacted on 1800 321324.
The Irish Travel Agents Association has contacted transatlantic carriers asking them to clarify the situation relating to travel arrangements and cancellations as soon as possible.
Yesterday, planes travelling to the US were recalled to the State when news of the attacks emerged. Some close to their destination had to divert to alternative locations - Aer Lingus flight EI 105 had to stop at Gandor, Newfoundland, and several flights landed elsewhere in Canada.
Aircrafts from European destinations were forced to divert to Ireland, keeping staff at Shannon and Dublin busy yesterday.
Dublin Airport was last night awaiting the return of several Irish flights and also dealt with a recalled British Airways flight and a flight which had set off from Moscow. However, Shannon dealt with the bulk of diversions.
A spokeswoman for Continental airlines confirmed that two flights, which depart daily from Dublin and Shannon, had to be diverted.
Aer Lingus also diverted a flight, which was on its way to New York, to Canada while one flight on its way to Los Angles returned to Dublin.
Delta airlines had only one flight destined for America, this flight which was travelling to Atlanta returned to Dublin airport.
A Royal Jordanian flight which had made a transit stop at Shannon airport was among the planes, destined for the US, which stayed grounded at the airport.
A flight to Seattle from London Heathrow was diverted to Belfast International Airport and landed safely at 5 p.m.
Belfast International Airport was last night on standby to receive rerouted Transatlantic flights.
A number of hotels in the area were asked to provide food and accommodation for the passengers.