There’s no indication when things might return to normal.

The UK is suffering a major disruption to air travel due to unspecific “technical issues” affecting flight control computer systems. Britain’s National Air Traffic Services (NATS) says it has “applied traffic flow restrictions to maintain safety,” with several airlines reporting disruptions felt at airports across the world. Hundreds of flights in and out of the UK have been delayed, according to The Guardian, with delays of up to 12 hours reported.

Despite the disruption, NATS says that UK airspace is not currently closed (as of 12:40PM UK time) during this very heavily traveled bank holiday Monday. NATS provided no indication for when the issue might be resolved.

Several airlines are reporting issues as a result of the system failure. According to Sky News, British Airways said it was “working closely with NATS to understand the impact of a technical issue that is affecting UK airspace, and will keep our customers up to date with the latest information.”

Scottish airline Loganair issued a statement to customers, calling it a “network-wide failure of UK air traffic control computer systems.”