Translink has launched an investigation and apologised after pictures showed a packed Dublin to Belfast service.
A passenger on 11.20am Friday train from Connolly Station raised the alarm after becoming concerned about the number of people on the train, DublinLive reported.
They said social distancing was practically impossible, that 16 people were either sitting on the ground or standing near the doors in their carriage and that people were drinking in the aisles, while many were not wearing masks.
A Translink spokesperson said today: " Translink and Irish Rail fully accept this situation was not appropriate during the Covid-19 pandemic and unreservedly apologise.
"We have managed public transport services safely during COVID-19 and continue to do so, however these were exceptional circumstances on Saturday, with a power failure on the railway line leading to reduced capacity on the 11.20 from Dublin. An additional relief train was operated between Dublin and Dundalk; however, whilst some customers transferred to this service, we accept that communication was not adequate regarding this.
"We are carrying out an investigation to ensure we learn from instances like this and are also reviewing our boarding and communications arrangements for passengers with our colleagues in Irish Rail," they added.
"Where services are busy, we do recommend that passengers allow additional time for their journey as it may be necessary to wait for the next train.
"We have a range of measures in place to ensure we all travel safely together. Details can be found here: www.translink.co.uk/covid19update
"The full Enterprise timetable will be restored on the Belfast to Dublin trains from today (Monday 31 August), offering customers more choice of travel times and providing additional capacity on the route."
