Some internet providers in Dublin and Belfast have been hit by interruption to service today.
The outage comes after two major underwater fibre cables in the Irish Sea were inadvertently cut.
The incident happened while tech company Cogent was carrying out emergency repairs on a submarine cable.
A repair ship has been dispatched and its expected the line will be back up and running by 3am tomorrow.
The outage is affecting many businesses and data centres as well as internet routed calls to UK mainland.