A major software outage affecting some NHS services across the UK was caused by a cyber-attack, it has been confirmed.
Advanced, a firm that provides digital services for NHS 111, said the attack occurred at 07:00 BST on Thursday.
The attack affected the phone service and referrals to out-of-hours GPs.
The National Crime Agency said it was “aware of a cyber incident” and was working with Advanced.
“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.”
Family doctors in London were warned by NHS England they could see an increased number of patients sent to them by NHS 111 due to the “significant technical issue”, industry magazine Pulse reported.
It said a letter to GPs in the capital stated the problem was affecting the electronic referral process for patients.
On Friday, the Welsh Ambulance Service reported the outage was “significant” and “ongoing”.
“There is a major outage of a computer system that is used to refer patients from NHS 111 Wales to out-of-hours GP providers.
“The ongoing outage is significant and has been far reaching, impacting each of the four nations in the UK.”
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.”