Irish Rail is advising people travelling by train to see Pope Francis in Knock that seats must be booked in advance.
Extra train services will operate on Sunday week next from Westport, Ballina and Athlone to Claremorris train station with a free bus transfer to and from Knock Shrine.
Meanwhile, people travelling to see Pope Francis in the Phoenix Park in Dublin are being advised to book their tickets quickly as some services are already sold out.
One train is already sold out on the Westport to Dublin line and one train on the Galway to Dublin line, and intending passengers are advised there's limited availability on other services, which should be booked as soon as possible.
There's still availability on the Sligo-Dublin service also.
Trains from Kerry and Waterford are already sold out
Irish Rail says advance booking is mandatory for all Intercity trains and no tickets will be available on the day.