The Health Service Executive has said it is taking precautionary action to protect its IT systems following a major ransomware attack on the NHS.
In a statement, the HSE said: "In light of the cyber attacks today on the information technology systems in both NHS and NHS Scotland, the HSE's leadership convened a special meeting this evening in order to consider the situation.
"On foot of that meeting it was decided that, as a protective measure, the HSE's Office of the Chief Information Officer would remove all external access to the HSE's Network to protect the integrity of clinical IT systems throughout our health system.
"A precautionary ‘major incident’ has been raised and the HSE will treat this as a ‘major incident’ during this time and until further information is known.
"The HSE will continue to monitor closely the situation and stay in touch with both NHS England and NHS Scotland to gather intelligence and offer assistance if necessary."
It is understood that the decision by to disconnect all external access to the network will prevent the HSE from receiving emails and cut all internet access over the weekend.
However, IT-based services that operate inside the HSE's own network and the Government's network will continue to work.
The HSE has issued precautionary advice to staff about how to prevent the system being infected, including telling them not to open any suspicious emails.
Those using any of the 1,500 PCs in the HSE system that still run on the now unsupported Windows XP operating system have been advised not to open any emails.
In any case where a machine becomes infected, HSE staff have been advised to turn the computer off and disconnect it from the network.
Sources say the HSE has not yet seen any attempts to get ransomware into its network, but attempts have been made to get it into the wider Government network.