In a statement released at 06:30 BST, the airport said the issue - which occurred in the early hours of the morning - had caused "widespread disruption" which was affecting flights from Terminals 1 and 2, BBC reported.
The airport said a number of flights had already been canceled and more were expected to be affected throughout the day.
The disruption comes at the start of the summer holiday season at the UK's third-busiest airport.
An airport source said the power cut "literally knocked everything off".
It has also affected other businesses in the surrounding area, including major logistics firms nearby.
SD/PR