The River Lee has burst its banks along the south channel in Cork City.
Gardaí say traffic diversions are in place in the area.
There is also flooding on Wandesford Quay, Morrison's Island, South Terrace, Union Quay and Father Matthew Quay.
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Motorists are being advised to use alternative routes.
Met Éireann reports that early tonight rain in the west will become heavy and then quickly spread eastwards. However the rain is set to clear later tonight.