Tens of thousands of air passengers have been stranded at Heathrow after British Airways cancelled all flights until Friday evening.
BA have cancelled about 500 flights
The move was prompted by an unofficial strike by ground staff in support of sacked catering workers.
More than 100 flights were grounded on Thursday leaving 15,000 passengers stranded - 1,000 of whom spent the night sleeping in the airport.
Union leaders said they were hopeful fresh talks may be held on Friday.
Mick Temple, managing director at Heathrow, said there would be "significant disruption today and probably for several days to come" for BA passengers, as the airline faces cancelling a total of 550 flights up until 2000 BST on Friday.
But the Transport and General Workers' Union said they were optimistic talks could take place on Friday afternoon with conciliation service Acas, and progress could signal the end of industrial action.
Earlier talks held on Thursday aimed at reinstating 600 sacked staff from the caterers that serve BA flights, Gate Gourmet, collapsed.
CHAOS AT HEATHROW
Wed am: Gate Gourmet brings in 130 temporary workers after sacking hundreds of its staff
Wed pm: The afternoon shift is sacked by a manager after workers missed a 20-minute deadline to report to work
Wed eve: BA cancel four flights from Heathrow to Hamburg and Paris because of lack of food
Thurs pm: Some BA staff stop work in sympathy with sacked Gate Gourmet staff
Thurs eve: BA cancels all long and short-haul flights out of Heathrow airport for the rest of day
Thurs night: BA cancels all flights into and out of Heathrow until at least 1800 BST on Friday, after talks with unions break down
Gate Gourmet director Richard Wells told the BBC: "What is happening here today is not about Gate Gourmet staff, it's the fact that BA staff are not working. They are taking unofficial action."
He denied being heavy-handed over the sacking of staff, saying they were spoken to and given written warnings before being dismissed.
He added that he had offered to meet with unions for further talks on Friday.
Brendan Gold of the TGWU said it did not condone the wildcat strikes by BA ground staff.
BA Chief Executive Rod Eddington said: "It is a huge disappointment to us that we have become embroiled in someone else's dispute."
He urged both sides in the row to resolve the dispute as quickly as possible to end travellers' misery.
Nearly 100 BA aircraft and 1,000 pilots and cabin crew are in the wrong places around the world, BA said.
Qantas, Sri Lankan, Finnair, GB and British Mediterranean, also serviced by BA ground staff, have also been affected by the strike which is taking place during the peak holiday season.
So far, three Qantas London-bound flights from Australia are known to have been diverted to Frankfurt.
BA said compensation claims will be considered on a case by case basis and all 70,000 passengers caught up in the chaos can rebook or have their flight costs refunded.
Staff at Heathrow - regarded as the world's busiest international airport - are trying to book travellers on flights with other airlines, while other services including Eurostar have reported a surge in business.
Meanwhile passengers due to travel on Friday are being urged not to turn up at the airport, but to contact the airline or their travel agent for more information.
BA, which is set to lose £10m for every day that the dispute continues, said about 4,000 passengers were put up at hotels across London and the South East on Thursday night.
Another 1,000 spent the night in Terminals 1 and 4, some staying in a huge marquee, and were provided with sleep rolls, blankets and food.
Those stranded were tired and frustrated on Friday morning, with many complaining of poor communication by airport staff.
AFFECTED AIRLINE NUMBERS
0800 727 800
0870 000 0123
Sri Lankan Airlines:
0208 538 2000
0870 850 9850
British Med Airlines:
0870 850 9850
Chuck Weinstein, 77, from Boston, and his partner, Janet Gorham, were returning to the US after a trip to Prague when their flight was cancelled.
Mr Weinstein said: "We went to a hotel. It was fine, slightly inconvenient.
"We have been here since 0530 BST and we are just waiting to see what's coming next and no one seems to really know anything.
"They're in the dark, they can only give out information as they are getting it."
The dispute began when Gate Gourmet dismissed 600 staff after an unofficial strike on Wednesday over the company's restructuring plans.
The dispute escalated when hundreds of BA baggage handlers, loaders and other ground staff represented by the TGWU staged an unofficial secondary walk-out.
Gate Gourmet has said it will not re-instate staff and said it had told the TGWU it was facing a financial crisis.
It said the actions of the staff had jeopardised the livelihoods of the entire 2,000-strong workforce.
But the TGWU said managers had provoked the dispute and the union was taking legal advice over the sackings.