Ireland's health service operator shut down all its IT systems on Friday to protect them from a significant ransomware attack the government said was carried out by an international cyber crime gang.

While the COVID-19 vaccination programme was not directly affected and the Health Service Executive (HSE) restored its test and tracing system within hours, hospital appointments have been cancelled across all outpatient services. "While it may take weeks to get all systems back, steady progress is being made, starting with services for the most urgent patients," Health Minister Stephen Donnelly said on Twitter.

Donnelly said hundreds of people were working flat out in response. HSE Chief Executive Paul Reid put the cost of rebuilding the IT system in the tens of millions of euros. Cancellations in parts of the country included radiotherapy appointments, cardiac checks, x-rays, CT scans and the processing of non-emergency blood tests as some hospitals were hit harder than others.

There was widespread cancellation of radiology services across the country due to its reliance on the IT system and particular challenges in laboratories, the HSE said. "Our system is much slower because we have to manually transcribe everything. We have people literally running around the hospitals delivering hand-written results," the HSE's Chief Operations Officer Anne O'Connor told national broadcaster RTE.

Some hospitals' information had been compromised, Reid said, adding that officials did not yet know the extent of the breach. Ransomware attacks typically involve the infection of computers with malicious software. Users are left locked out of their systems, with the demand that a ransom be paid to restore computer functions.

The government has said it will not pay any ransom. "I can't overstate the impact of this attack on our ability to do our jobs since Friday," Doctor Gabrielle Colleran, head of radiology at Dublin's National Maternity Hospital said on Twitter, posting a photograph of a blank computer screen.

"I can't imagine what kind of person thinks I'll attack the systems providing healthcare to kids... This makes me beyond angry."