Rail services have been suspended between Dalkey and Greystones 'until further notice', Irish Rail has confirmed.
The company says the line will be closed for the weekend 'at least'.
It follows a fire at a signalling equipment room in Bray at around 11.30pm last night.
The fire is believed to have started within the relay room, and was not the result of criminal damage or vandalism.
As a result of the fire, DARTs are suspended between Dalkey and Greystones, with Dublin Bus accepting rail tickets.
People are being advised to transfer to bus services at Dun Laoghaire.
Meanwhile, Dublin Connolly to Rosslare Europort services will have bus transfers between Connolly and Greystones.
Iarnród Éireann has apologised for any inconvenience caused.
In a statement, they said: "Signalling teams are assessing the damage and repairs required, but have indicated that services will remain suspended at least for the remainder of the weekend (Saturday 19th and Sunday 20th May)."
âš ï¸ Bus transfers between Connolly and Greystones for services between Connolly and Rosslare Europort.
DART services are operating between Dalkey and Howth/Malahide - some minor delays possible.
Full information will be updated here and at https://t.co/YCsDqRZyyr
— Iarnród Éireann (@IrishRail) May 19, 2018
