A Brussels airport spokeswoman said the outage hit at 5am BST on Thursday and specifically affected the luggage and air conditioning systems.

Hundreds of passengers were left outside the terminal at dawn before being allowed inside around two hours later.

"There was no communication at all so nobody knew what was going on," said passenger Karolien Coenen, who missed her morning flight to Barcelona.

Passenger Daniel Stas arrived at dawn and said: "There was no electricity at all in the airport so we could not check in. Everything was blocked, computers were blocked, it was a real total blackout."

All systems were back to normal by mid-morning, but by then the backup was such that it would affect schedules for the rest of the day.

"The system dealing with the luggage is extremely complex, it took time to restart it so several passengers have not been able to get their luggage back or to leave with their luggage," spokeswoman Florence Muls said.

Despite the delays, the airport warned passengers to show up on time, adding that incoming flights should not be affected.