ESB Networks is appealing to residents all over Cork to conserve electricity today, as they try to get customers back online after power outages caused by flooding.
A major clean-up is underway across Cork city and county after an estimated 50 millimetres of rain fell overnight, causing many rivers to burst their banks.
Among the worst affected are Douglas, Blackpool, Glanmire and Clonakilty - where around 700 households are still without power this morning.
While the worst of the rainfall is thought to be over, there are concerns about the impact of high tide on a flooded Clonakilty at lunchtime today.
The river Feale burst its banks in the west Cork town at around 2am this morning.
Motorists have been warned that there is no access in or out of the area for now.
More than 50 homes and many businesses were flooded and several thousand left without power and council bosses said pre-emptive action helped reduce the impact of the overnight flash floods which left more than a dozen areas under water.
Emergency services in the city received 128 calls for help following floods, including 45 callers needing direct rapid response.
Met Eireann said the rain, including thundery downpours and hail, is expected to move north across the country today after torrential showers dumped up to 70mm locally in some parts of Cork.
Forecasters said heavy rain fell between 8pm and 3am on top of already saturated ground, compounding the impact of torrential showers.
Cork City Council said 20 homes were hit by the floods in Park Court, Ballyvolane, and another eight in the Commons Road area.
Also in the city the authority said a significant number of properties, business and residential, in Blackpool Village and Watercourse Road were inundated in the early hours of the morning.
Elsewhere, the council said localised flooding was reported on the Old Kinsale Road near the business park, Sarsfield Road roundabout, Monaghan Road, Centre Park Road and Turner’s Cross.
“The council’s advance work in gully cleaning throughout the city assisted in preventing more localised incidents of flooding,” officials said.
Across the county Douglas and Clonakilty were worst hit.
Up to a metre of water was reported on the main streets of Douglas village with 3,000 homes without electricity, while officials warned there was no access in or out of Clonakilty.
Glanmire on the edge of Cork city was also badly hit.
Cork City Council said its flood emergency response plan swung into effect at 3.30am and the crisis management team met at 7am.
It said staff from the fire and emergency services and roads and drainage units followed a swift and co-ordinated response to incidents throughout the morning.
“All council services associated with a flood response continue to be activated and will continue throughout the day to respond where required,” a spokesman said.
Weather and river levels will also be monitored through the day.
The deluge occurred after several hours of rain across Belfast and parts of counties Down and Antrim left 1,000 homes without power and 700 people needing the help of emergency services.
Most main routes in south and east Belfast were impassable overnight, after heavy rain caused severe flooding.
Cars were submerged during a massive downpour yesterday evening.
A thousand homes lost electricity temporarily and families battled frantically using boards, brushes and sandbags to try to keep back the rising waters.
Even a police vehicle in West Belfast was submerged and officers had to be rescued from the rooftop.
The areas worst affected were South and East Belfast, Dunmurry, Lisburn, Bangor and the North Antrim village of Cushendall.
More torrential downpours and floods are forecast for this afternoon.
Drivers are being urged to be extremely careful because manholes have been dislodged.
Parents have also been advised to know where their children and ensure they stay away from areas hit by flooding.
Northern Ireland Water dealt with almost 3000 calls and got reports of blocked sewers and external and internal flooding.
Politicians are urging it to spend on improving the drainage system.
Belfast City Council has established an emergency incident centre and the clean-up is going on, though there are fears of more floods later.