Parts of Cork city and county have been left under several feet of water after flash floods overnight.
Met Eireann reported that 50mm of rain fell between 8pm and 3am on already saturated ground as thunderstorms swept in from the south.
Locally the figure may have been as high as 70mm.
The worst affected areas included Douglas on the outskirts of the city, Carrigaline, Blackpool, Togher, the Kinsale Road and a stretch of the South Ring Road.
Council chiefs have put a flood response plan in place.
The army were called out to help an ambulance stuck in a flood on the N71, but it will be hours before the clean up can begin.
Forecasters warned there will be further rain today but it is not expected to be as heavy as overnight.
Elsewhere there were reports of more than 1,000 homes in Cork without electricity.
The Met Eireann forecast for today is for a band of heavy rain, with embedded thunderstorm activity and hail, to continue to move northwards this morning producing further flooding.
Drier weather will follow with some sunny spells developing, it said.
Meanwhile, other parts of the country have also been hit by flooding this morning.
Dangerous conditions have been reported on the the M7 already where a car has overturned at the Athy junction in County Kildare, while there have been a number of other flood-related incidents between the Naas North and M9 junctions.
A car has become stuck under a railway bridge on the Ballymahon road in Meath because of flooding, and in Tipperary, the M8 Dublin/Cork Rd is flooded between the Cahir South and Mitchelstown North junctions, but it is not yet closed.