Update 9pm: Dozens of homes have been flooded in a Co Laois town after three rivers burst their banks.
Flash floods wreaked significant damage in Mountmellick on Wednesday as torrents of water ran through the town.
The floods poured into multiple properties.
Laois County Council triggered an emergency plan, evacuating many residents to nearby hotels.
Civil Defence and Fire Service crews were involved in the relief efforts.
All roads in the town were impassable during the height of the flooding.
The episode unfolded after sustained rainfall on Tuesday night and early Wednesday morning.
Councillor Paddy Bracken described the scenes as "mayhem and disaster".
"It's a shocking situation here in the town, never saw anything like it before," he told RTE.
"I'm a long time knocking around and I have never seen anything like this - I seen flooding in the 1990s but nothing as bad as this. It's unreal."
The council has warned residents in nearby Portarlington to take precautions against potential further flooding on Wednesday night.
Update 8pm: At least 20 families have been evacuated from their homes in the Co Laois town of Mountmellick.
It is after the Owenass River burst its banks earlier.
The flooding is affecting two housing estates in the town.
Dozens of homes in Mountmellick, Co Laois have been flooded after the Owenass River burst its banks. | Read more: https://t.co/Xutxl6TjIp pic.twitter.com/LsepmSiDxT— RTÉ News (@rtenews) November 22, 2017
A status yellow rainfall warning remains in place for Munster and Leinster until 9 o’clock tonight.
Many parts of the country experienced heavy rain all day leading to major delays on roads like the N3 and M4.
Update 4.15pm: Gardaí warn motorists not to drive through flooded roads
Gardaí have warned people to use alternative routes if the road they are travelling on is flooded.
They have warned that people should not drive through flooded roads as even when they appear shallow it could be deeper.
Earlier today, AA Rescue said many cars have been damaged by driving through floodwater as today’s heavy rain causes major traffic jams.
The gardaí have warned against taking unnecessary risks stating a half foot of fast-moving flood water can knock over an adult, while it can take just a half foot of rushing water to carry away a small car and two feet of rushing water can carry away most vehicles.
They have told motorists to take extra care at night when it is harder to see flood dangers and drive to the road conditions.
A status yellow rainfall warning remains in place for Leinster and Munster remains in place until 9pm Wednesday night.
Laois County Fire & Rescue Service captured this footage this morning, as many areas were hit with floods | More: https://t.co/Xutxl6TjIp pic.twitter.com/TWlh6vGWSw— RTÉ News (@rtenews) November 22, 2017
Gardaí in Dublin have announced a number of roads have been affected by flooding.
Update - 11.50am: AA advises motorists to slow down as floods hit and temperatures set to drop
The AA is advising motorists to slow down and allow extra journey time as they report dozens of flood-related breakdowns across Dublin and Leinster this morning.
AA Rescue said many cars have been damaged by driving through floodwater as today’s heavy rain causes major traffic jams.
Many roads in Dublin, Kildare, Kerry, Limerick, Clare, Waterford and Tipperary are flooded.
This morning alone the breakdown assistance provider had already received more than 20 flood-related breakdown call-outs.
Conor Faughnan of the AA said: "By 10am on Wednesday we had already been called to attend to 25 flood-damaged vehicles.
"It’s important that motorists in flood-affected areas avoid driving through larger pools of water where possible as it’s easy to be deceived about how deep the water is. It’s simply not worth the risk as you can very quickly find yourself stuck on the roadside."
#DUBLIN Traffic is down to one lane on the #N3 Navan Rd inbound at J2 Blanchardstown due to flooding, with delays back to J5 Dunboyne. Photo Credit: @Paul_Hearns https://t.co/pdsEzJTRQr pic.twitter.com/bfshs6OrC2— AA Roadwatch (@aaroadwatch) November 22, 2017
They have also advised motorists to drive with extra care in the coming days, as an expected drop in temperatures could bring ice and frost across the country.
Mr Faughnan said: "In the coming days a drop in temperatures is likely to wreak havoc on car batteries, particularly if they’re older or weaker.
"So it’s important that motorists give their car a quick check today before conditions take a turn for the worse from tomorrow."
Motorists are also being urged to be on the lookout for vulnerable road users, such as cyclists and pedestrians, and to ensure their windows and mirrors are adequately cleared before beginning any journey in order to improve visibility.
Mr Faughnan also said today's rain means the risk of icy patches is greater as roads are still going to be wet.
Earlier: A number of roads around the country are impassable due to flooding and the river Tolka has burst its banks on the N3 in Dublin.
Met Eireann has issued a status yellow rainfall warning for Munster and Leinster until 9pm tonight with widespread heavy showers this morning.
Temperatures are expected to drop significantly later today with chances the rain could turn to sleet.
Forecaster with Met Eireann John Eagleton has confirmed that winter is here.
He said: "We're in a colder regime, it has been very mild for the past 10 days or so, but I think that is all going to change.
"I think it is over the next three or four days that we will see much colder weather coming in from the north, maybe later this morning and in the afternoon.
"For the rest of the week temperatures are going to stay low. Winter has finally arrived."