A major cyber attack has caused a software outage at the NHS 111 service.
Users are being warned to expect delays as staff have reportedly resorted to using pen and paper to record cases.
The system was shut down by hackers thought to be linked to a hostile state and cybercrime experts have been drafted in to investigate.
Advanced, the firm which provides digital services to the 111 service, said the attack was first noticed at 07:00 BST on Thursday.
The system supplies software to 85% of NHS services.
Officials believe the fallout will last until Tuesday at the earliest, with the public told there will be delays when ringing the hotline.
It’s feared disruption could drive patients to overstretched accident and emergency departments over the weekend.
This was the case in the Isle of Wight on Friday, when the Isle of Wight NHS Trust declared a criticial incident in response to ‘sustained pressure’ on its A&E services.
More than 1,000 care homes which use the firm’s Caresys software have been impacted, as well as mental health services across the UK.
Pharmacies confirmed calling NHS 111 for emergency out of hours prescriptions will also be affected.
The National Crime Agency said it was ‘aware of a cyber incident’ and was working with Advanced.
An NHS source said: ‘At the moment, call-handling and response times are holding up but there is a concern that the situation may change over the weekend, and that we could see a deterioration.
‘Cases in need of an ambulance are being prioritised.’
The source added NHS 111 call handlers are using alternative systems to send ambulances to people in need.
On Friday, the Welsh Ambulance Service confirmed its callers would take longer to respond to NHS 111 calls and this would impact patients into the weekend.
NHS England warned family doctors in London they could see increased numbers of patients sent to them by NHS 111 because of the issue.
An NHS spokesperson reiterated disruption was currently at a minimal, saying: ‘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.’
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