Piles of suitcases caught on camera by a baggage handler at Heathrow
Check-in desks at Heathrow Terminal 5 have reopened following problems with luggage conveyor belts that caused major disruption.
Thousands of passengers were delayed, with some saying they had to queue for hours. Others had to rebook or board flights without their luggage.
Airport operator BAA blamed a mechanical failure which was resolved.
But one passenger told the BBC that as many as 60 travellers were forced to spend the night at the airport.
British Airways apologised for the inconvenience and said it was doing everything it could to minimise disruption.
The airline said no flights had been cancelled as a result of the problem and had hoped its customers could fly on Sunday night.
But Rob Mortimer, who missed his flight to New York because of check-in delays, said he and dozens of others were forced to sleep in the airport without any help with bedding or hot drinks from BAA.
"There were probably about 50 or 60 people that I could see just bedded down on the cold, hard floor," he said.
"Every time I went to ask they said the hotel rooms had already been given out to the most deserving cases. They said we could sort out our own hotel, but they were all fully booked anyway because of what happened at Terminal 5."
Mr Mortimer was due to fly out of Heathrow on Monday morning.
"I know it's BAA's fault really, but I've travelled so much with BA and I must say I am disappointed," he said.
Mr Mortimer had been due to start a new job in New York, and was relieved that his new employers accepted he would not be there on time.
BAA said it was confident that all disrupted passengers would be able to fly out of Terminal 5 on Monday.
Some queued for hours before being told they were in the "wrong" queue
But some of those affected faced considerable expense to change their plans, including Nial O'Connor, from London, who was due to fly from T5 to Marseille on Sunday.
However, after his luggage went missing, he rebooked his flight with BA and was given one flying out of Gatwick on Monday.
He said the change of plan has cost him an extra £80 to rebook the flight, £130 on a taxi and more on a hotel.
Mr O'Connor was told his luggage would be flown out to Marseille separately.
He told the BBC he was very angry and had found BA unhelpful.
Barry Goldstone, who was due to fly to Denver with BA on Sunday afternoon, described the scene at the terminal as "absolute chaos".
"They [BA] don't seem to have any continuity plan if anything goes wrong, and unfortunately they don't seem to have any consistency of information either."
One baggage handler said at one stage there had been more than 1,000 pieces of luggage piled up, and described the situation as "absolute chaos".
A BAA spokeswoman said on Sunday night: "We are working hard with our colleagues at British Airways to help passengers to continue their journeys.
"We hope that passengers wishing to depart tonight will be able to do so and we are sorry for the obvious inconvenience to travellers and British Airways."
A BA spokesman said: "As a result of the problem some passengers have been unable to check in bags. Check-in has now reopened but there will be some delays.
"We apologise to our customers for the inconvenience. We are doing everything we can to minimise disruption."
The terminal was hit by problems when it opened in March 2008, with flights cancelled and thousands of bags lost.