"I would estimate, given the timing of the bank holiday weekend, that this has affected a hundred flights and a thousand passengers already", said John Strickland, director of aviation at analysts JLS Consulting. However, the BA was forced to clear the entire schedule and admit that further delays could disrupt travel in the coming days.
Following a "major IT system failure" that "is causing very severe disruption to our flight operations worldwide", the airline says that flights will have to be grounded until the problems are resolved.
BA says affected passengers will be offered a rescheduled flight or a refund, though judging by the amount of ire being shown on social media at the moment, that might not be enough.
"There are a significant number of bags at Heathrow which we will be reuniting with customers via couriers as soon as we can".
Alex Cruz, the chairman and chief executive of BA, part of Europe's largest airline group IAG (ICAG.L), said there was no evidence of any cyber attack.
Stranded holidaymakers spent the night on yoga mats on airport floors as disruption from the British Airways system failure continued into a second day.
Dan Abrams wrote that it had taken him three hours just to leave Heathrow's Terminal 5, adding that there was "total mayhem here".
Long-haul flights into London are expected to arrive as scheduled on Sunday, British Airways said in an emailed statement. "No way we'll make our Vegas flight", wrote one passenger David Raine wrote on Twitter.
London's Heathrow Airport one of the world's busiest said it was working with BA
"At this stage we are aiming to operate a near normal schedule of flights from Gatwick and the majority of our Heathrow services", it said.
At Gatwick frustrated passengers could be seen surrounding BA staff at the check-in as they handed out letters which apologised for the cancellations and gave details about how to claim for hotels, local transport and refreshments.
However it urges customers to only come to the airport if they have a confirmed booking for travel.
Heathrow Airport spokesman announced: "An issue with a worldwide British Airways' IT system is causing some delays for passengers at Heathrow this morning".
The IT crash caused chaotic scenes in Heathrow and Gatwick on Saturday, with passengers complaining they had been left in the dark by the airline.
"We are extremely sorry for the huge inconvenience this is causing our customers and we understand how frustrating this must be, especially for families hoping to get away on holiday", Cruz said.
This story will be updated as more information becomes available.