NHS 111 staff across the UK were left using pens and paper after a major cyber attack was carried out.
People seeking medical help via the service are being warned of delays due to a “major” computer system outage caused by the attack.
It affected the phone service and referrals to out-of-hours GPs.
The issue was identified at around 7am on Thursday, August 4.
Security services in the UK are investigating following the incident.
Software and services provider, Advanced, said the issue may not be fully resolved until next week.
“A security issue was identified yesterday, which resulted in loss of service,” said Advanced boss Simon Short.
“We can confirm that the incident is related to a cyber-attack and as a precaution, we immediately isolated all our health and care environments.
“Early intervention from our Incident Response Team contained this issue to a small number of servers representing 2% of our Health & Care infrastructure.”
An NHS spokesperson said there was currently minimal disruption and it was monitoring the situation.
“NHS 111 services are still available for patients who are unwell, but as ever if it is an emergency please call 999,” they said.
“There is currently minimal disruption and the NHS will continue to monitor the situation as it works with Advanced to resolve their software system as quickly as possible – tried and tested contingency plans are in place for local areas who use this service.”
A spokesman for the Scottish Government said it was aware of reported disruption to one of NHS Scotland’s IT suppliers’ systems,
It said that it is “working with all health boards collaboratively on a four nations basis with the National Cyber Security Centre and the supplier to fully understand potential impact”.
The Government also stated that “continuity plans” are in place.