More than a quarter of a million homes and businesses suffered power cuts as hurricane-force winds swept in from the Atlantic.
Initially, 100,000 homes and businesses – mainly along the south and south-west coasts – suffered blackouts, but last night the number had more than doubled.
ESB said it had 2,100 separate faults reported across its network from falling trees, debris and telegraph poles.
Meanwhile, more than 10,000 communications faults were reported to Eircom. About 200,000 homes and businesses were expected to be without power overnight.
Jerry O'Sullivan, ESB Networks managing director, said: "We are dealing with a situation that is as bad if not worse than anything that we have seen in the past decade."