In farcical scenes, airport staff have been forced to write flight information on whiteboards in the middle of departure lounges.
The malfunctioning caused a "handful" of people to lose their flights, Metro quotes the airport saying.
Photos and videos posted on social media showed airport staff updating flight information by listing flight numbers, destinations, status, and gate numbers in black, red and green ink, and rubbing the writing out and updating with new information as they came in.
A spokesman said the information boards stopped working "earlier this morning" but was unable to give a precise time.
Gatwick says the electronic boards were displaying incorrect information because of a damaged fibre-optic cable, and it expects telecom provider Vodafone to "resolve the issue soon".
Ayla Herbert, 26, from Penryn, Cornwall, was at the airport for a Flybe flight to Newquay when she encountered a crowd gathered around two whiteboards after passing through security.
The problems have been going on for at least three hours at one of the UK's busiest airports. "This is a top priority for us", it said. "They used megaphones to tell everyone of updated information". Contingencies are working - we have whiteboards and friendly staff on hand to help, and tens of thousands of passengers have departed on time. "We are keeping Gatwick Airport constantly informed of progress".