Update 7pm: Passengers on a train that hit a herd of cows near Tullamore are being provided with a replacement bus and train service.
The 3.35pm train was travelling between Dublin and Galway when it hit up to eight cows.
The original train will continue to Portarlington with almost 200 passengers on board.
They will be bussed from there to Athlone where they will board a train to Galway.
Passengers on the 3.05pm Galway to Heuston train will be bussed from Tullamore to Heuston.
It is understood that the cows have been cleared from the tracks.
Update 5.51pm: Irish Rail says delays are expected on Galway and Westport services after a train hit a herd of cows.
It happened near Tullamore, Co Offaly earlier on a Heuston to Galway service.
The rail operator says significant delays are expected as a result.
Update: 15:35 Heuston Galway remains stopped near Tullamore after striking a herd of cattle. Services to and from Westport and Galway are experiencing significant delays as a result— Iarnród Éireann (@IrishRail) June 28, 2018
Up to eight cows have been badly injured.
The train is still at the scene and has been badly damaged.
Barry Kenny from Iarnrod Eireann says services to and from the West will be disrupted;
"The train is stopped and can't move at this particular point in time," he said.
"We're dispatching maintenance personnel to the site. We're also dispatching customer service personnel because what we want to do because the delay is significant is get the people on board off the train if it is safe to do so.