Rail services between Dalkey and Greystones in Co Wicklow have been suspended until Monday morning.
The disruption is the result of a fire at a signalling station in Bray, which broke out around 11.30pm on Friday.
It is believed the fire started within the relay room at the station and was not a result of vandalism or criminal damage.
Signalling teams are assessing the damage and have indicated that services will remain suspended at least for the remainder of the weekend.
Dart services are in operation between Dalkey and Howth/Malahide, although some minor delays are possible.
An Irish Rail statement read: “Due to the extent of damage, services will not be restored until Monday morning at the earliest.”
Dublin Bus will be accepting rail tickets and customers are being advised to transfer at Dun Laoghaire.
Commuters travelling to Rosslare Europort will have bus transfers between Connolly and Greystones.