Thousands of customers are experiencing power outages and disruption to services due Storm Ophelia.
According to the ESB, approximately 330,000 electricity customers remain without power across the country.
While telecom provider eir estimates there are over 11,000 customers without broadband, telephone and mobile services.
This includes damage to poles, cables and mast infrastructure.
The company expects the number of customers affected to rise significantly.
It says the damage will likely be extensive and repair work will take time.
"There are currently 90 mobile sites off air, with the worst affected areas so far in the Southwest, West and Midlands."
The ex-hurricane battered Connacht and Leinster before striking Ulster.
The public is being asked to stay indoors.
It is thought hundreds of thousands of homes could be without power for days.
ESB map shows areas of supply disruption | Source: ESB
Coastal areas are at risk of flooding this evening.
ESB spokesperson Bernadine Moloney said some could be without power for up to 10 days.
"The majority of people who are without power right now will be without power overnight and for the next couple of days and about 5% or 10% of people will still be without power ten days from now," she said.
"People need to make preparations.
"Particularly people who have any vulnerable medical conditions, they need to make arrangements with their medical providers and if they need electrical medical equipment in their home they need to make alternative arrangements."
She warned all members of the public to avoid any fallen power lines.
She said the lines remain live and are extremely dangerous - adding that they can be reported by calling the ESB on 1850-372-999.
Customers are advised to check the powercheck website and follow the ESB twitter account for updates on repairs and restoration times throughout the day.
Ms Moloney said there is no need to contact the ESB if the power-outage affecting your area is already logged on the powercheck website.
Additional reporting: Jack Quann