Over 2,500 homes and businesses in the Shannonside region are without power this afternoon.
Areas affected include Newtowngore and Mohill in Co Leitrim; Drumlish, Ardagh and Ballymahon in Co Longford; Athlone; and Mantua, near Elphin, in Co Roscommon.
The ESB said: "The majority of customers without power have been affected by an overnight fault (around 4am) on a medium voltage line in the Co Longford area.
"Other pockets of customers have had supply interrupted as windy conditions and lightning have caused some damage to parts of our network today.
"All available ESB Networks crews are mobilised to restore power to all customers as soon as possible.
"We acknowledge the disruption to family and commercial life this causes and thank our customers for their patience as our crews work to safely restore power."
