The HSE has shut down all of its IT systems after a "sophisticated" cyber attack overnight.
The executive is liaising with Gardai and the National Cyber Security Centre to assess the extent of it.
Community Healthcare West has confirmed to Midwest News that Covid-19 testing across the region is not affected by the cyber attack.
The National Ambulance Service isn't affected - with 999 calls still being answered and responded to.
Elsewhere, The Rotunda Hospital has cancelled most outpatient appointments, except for heavily pregnant women.
HSE chief executive Paul Reid says Covid vaccinations are also going ahead as normal.