The HSE says the recent rise in demand for Covid testing is being driven by children under the age of 14.
Walk-in test sites across the country have been suspended after long queues formed over the last few days.
The HSE says demand for walk-in tests at the centres in Dunmanway and the City has been strong and is leading to long waiting times for a result.
People are being asked to book an appointment online instead.
Niamh O'Beirne, the HSE's national lead for testing and tracing, says young people are behind the increasing demand.
"It's to do with the volume of children under 14 who are presenting for testing, we have really high volumes through walk ins and self referrals, in the past 7 days we've had over 25,000 children in this age group come in for testing.
"In the interests of the children so they don't have to stand in a queue, especially in the warmer weather, it's much better if they can book an appointment time and show up for that time."
