A section of the main Dublin to Belfast railway line has collapsed in north Dublin.
It happened last night north of Malahide station on the viaduct across the estuary.
Iarnród Éireann said damage to the line had been caused by subsidence at an embankment.
It was spotted by train driver travelling from Balbriggan to Dublin. The train had passengers on board but he managed to stop.
The line has been closed and there are currently no northern commuter and Belfast enterprise trains running as a result.
Customers are advised to travel by bus and bus transfers are being arranged for Dublin/Belfast train services.