The incident happened at the Howth Junction at around 6.20am this morning, halting services between Howth, Malahide and Harmonstown.
There is severe disruption to Dart and commuter rail services as emergency services attend a "tragic incident" at Howth Junction.
A spokesperson for Irish Rail said: "There is now no DART service between Killester and Malahide/Howth.
So while Dublin Bus will be accepting rail tickets there will be increased pressure on their capacity and customers may need to consider making alternative arrangements".
Irish Rail have also confirmed that they expect the disruption to continue throughout the morning peak.
He added that the Dublin/Belfast Enterprise will have bus transfer between Connolly and Drogheda.
Southside DART services are still running.
Irish Rail Spokesperson Barry Kenny said on RTE Radio One's Morning Ireland: 'It would not be unusual for the line to be closed for two, two-and-a-half hours.
"There will be major disruption for the entirety of this morning's peak, this means no DARTs operating from Malahide or Howth".
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