British Airways has said it has been forced to cancel almost all its flights from UK airports on the first day of a strike by pilots.
"After many months of trying to resolve the pay dispute, we are extremely sorry that it has come to this," BA said in a statement.
The airline said it remains willing to return to talks with the British Airline Pilots Association (BALPA).
"Unfortunately, with no detail from BALPA on which pilots would strike, we had no way of predicting how many would come to work or which aircraft they are qualified to fly, so we had no option but to cancel nearly 100% of our flights."
The UK flag carrier and its 4,300 pilots have been locked in a nine-month pay dispute that could disrupt the travel plans of nearly 300,000 people.
Pilots are to continue their strike tomorrow and are threatening to strike for one more day on 27 September and then possibly again closer to the winter holidays should the dispute rage on.
Anyone flying with the airline to and from Ireland are encouraged to check their flight status before travelling.
Travel Extra editor Eoghan Corry said the strike will have vast implications, affecting around ten thousand Irish passengers.
Mr Corry explained that eight British flights to Heathrow have been cancelled, today and tomorrow. However, routes that are out on contract are operating.
This includes the London City service from Dublin, which is contracted to Stobart.
.@British_Airways flights are affected by a pilots strike taking place today and tomorrow. Passengers are advised to check latest flight information with their airline before travelling to @DublinAirport. More details here: https://t.co/XyJNzkJysK— Dublin Airport (@DublinAirport) September 9, 2019
"The only things that are flying are some of the routes that are out on contract. While we've lost eight British Airways flights to Heathrow today and tomorrow - all of them cancelled: the first was at 7.10am, the last is at 9pm tonight, but it means that the London City service, which is contracted out to Stobart, is flying as normal.
"It's one of the few parts of the whole British Airways operation that is flying as normal."
Mr Corry said BA's long haul service has come to a halt - apart from two services from Gatwick to New York - but added that we should not underestimate the ability of airlines to cope with these kind of situations.
BALPA has rejected a pay increase of 11.5% over three years that the airline proposed in July.
BA says the offer would see flight captains receive "world-class" pay and benefits of around £200,000 (€220,000) a year.
It also points out that two other unions representing 90% of the airlines' workers have accepted the 11.5% raise.
BALPA counters that co-pilots' salaries average around £70,000 and that of junior ones drops down to just £26,000.
This leaves some in heavy debt since they must first undergo training that the BBC estimates costs around £100,000.
BALPA also points to a nearly 10% jump in pre-tax profits reported by BA's parent company IAG last year.