The key areas affected are Counties Fermanagh, Armagh and Down with the Newcastle, Kilkeel and Rostrevor areas with the highest number of faults.
Customers can call our helpline on 03457 643 643, visit our website or follow us on Twitter @NIElectricity for updates.
Sara McClintock, NIE Networks’ Communications, said: "We’re working as fast as possible to restore electricity to the homes and businesses without power. We are working on around 200 individual network faults – each of these may require the co-ordination of engineers, tree cutters, excavation and repair teams.”
NIE Networks is also reminding customers:
• never approach broken lines or damaged poles, and keep children and animals away - report damage to NIE Networks on 03457 643 643 and listen to recorded messages carefully
• if you are using a generator, be careful where you site it in case of carbon monoxide poisoning
• turn off electric cookers, ovens, irons, etc. if electricity supply is lost
• leave a light switched on so you know when power has been restored
• take extra care if using candles, oil lamps or other naked flames
• test smoke alarms with fresh batteries
• ensure adequate ventilation if using gas heaters.