All trains in and out of Dublin Heuston have been delayed after a points failure between Kildare and Portarlington.
The Dublin to Galway service has been delayed by about 45 minutes tonight.
Irish Rail spokesman Barry Kenny says the company is sorry for the situation.
"We'll get trains moving straight away and those delays will ease very, very quickly," he insisted.
There are crews working to fix the "infrastructure fault", Mr Kenny added, apologising for the inconvenience.