The Central Applications Office has urged students and others trying to log on to its website to be patient and keep trying.
Third level applicants and their teachers have experienced severe difficulties trying to log on to the site this morning - just two days before the deadline for CAO applications.
The CAO has blamed the volume of traffic for the difficulties. But it says the system is functioning and applicants will eventually get through.
However, career guidance teachers have told RTÉ they are not even managing to get into the site.
One school in Limerick tried to send in an application for an hour and a quarter this morning with no success.