The HSE has suspended walk-in Covid testing at centres nationwide due to a surge in demand over recent days.
Officials are aiming to reduce queues at testing sites after demand rose by more than a third in the last 48 hours.
The increase is being driven by under-14s coming forward for testing following the return of schools.
Niamh O'Beirne, the HSE's national lead for testing and tracing, said people will now need to book a test in advance.
“We're pushing all of our capacity, which is about 20,000 nationally, to be made available through online booking or through the GP network,” she said.
“We're asking people to go online and book their test, rather than walk up. This will enable everyone to get an appointment, but also allow us to manage the queues onsite.”
To book a Covid test online, visit covid19test.healthservice.ie/hse-self-referral
