The HSE says the suspension of walk-in Covid testing centres could last for the next two weeks.
It's aiming to reduce queues at sites after demand rose by more than a third in the last 48 hours.
The increase is being driven by under 14s coming forward following the return of schools.
Niamh O'Beirne, the HSE's national lead for testing and tracing, says people will need to book a test for the next while:
"What we're doing is that we're pushing all our capacity that's available on our sites, which is about 20,000 nationally, to be made available online or through the GP network and close contact referrals.
"It just means we're asking people to go online and book their test instead of just walking up, and this will enable everybody to get an appointment but also to be able to manage the queues onsite."
