Earlier today, British Airways (BA) has canceled all flights out of London's two biggest airports, Gatwick and Heathrow, following what the company described as "catastrophic" and "a major IT system failure."

Issues started appearing in the morning, but while BA officials hoped to resolve the problem, at 16:45 GMT, the company published a statement and announced it had to cancel all flights out of London for the remainder of the day.

Flights coming into London are expected to land as normal, and the company said traffic would resume as normal tomorrow, Sunday, May 28.

BA: It's not a cyber-attack!

BA has declined to reveal details about the mysterious IT outage but said it wasn't a cyber-attack. According to a BA spokesperson, the mysterious issue also affected its call center and website, not just computers handling flight information.

Furthermore, without access to BA flight data, baggage sorting for BA passengers was down for most of the day.

Passengers were stuck in planes and the airport for hours, waiting to take off or just pick up their luggage and go home. BA offered to reschedule or refund flights.

The outage couldn't have come at a worse time, as this was one of the busiest weekends of the year, coinciding with the half-term break for many UK schools. This is also an extended weekend in the UK, also known as the Late May Bank Holiday, a period where many hoped to travel abroad.

Union blames outage on BA outsourcing IT work to India

GMB, one of the UK's biggest unions, blamed the outage on BA outsourcing a huge chunk of its IT work to India.

BA's image and profit took a big dip, as other airlines were completely unaffected. Some passengers skipped to another airline's flight, while others that couldn't find a spot, vented their anger on social media.

Update [May 28]: BA officials blamed the outage on a power supply issue. Flights out of London resumed today, but with some cancellations and delays.