The incident will likely have an impact on local A&E departments.
NHS 111 has been hit by a cyber attack leading to a “major” systems outage.
Advanced’s Adastra software, which handles patient demographics, appointment bookings, home visits, and dispatches ambulances, was one of the systems hit by a cyber incident on Thursday morning.
Caresys software which provides patient records systems to other areas of the NHS and care homes, has also been affected.
The firm is reported to provide software to around 85% of NHS 111 providers and some ambulance services.
The outage has left NHS 111 staff “working on paper” and is “negatively affecting” response times, according to a letter from NHS bosses sent to London GPs.
It is not known at this time if patient records were breached, but the incident will likely have an impact on local A&E departments.
The Welsh Ambulance Service has described the outage as “significant”, “major”, and “far reaching” and warned it was affecting all four nations.
An NHS spokesperson said: “NHS 111 services are still available for patients who are unwell, but as ever if it is an emergency please call 999.
“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 spokesperson for the Scottish government said it is “working with all health boards collaboratively on a four-nations basis with the National Cyber Security Centre [NCSC] and the supplier to fully understand potential impact”.
A spokesman for Northern Ireland’s Department of Health said they are working to keep disruption to a minimum.