The NHS is investigating "an issue with IT" amid reports of a cyber attack on its systems.
Hospital trusts and GP groups in Lancashire and Hertfordshire were among those reporting problems, with one warning patients to only visit hospital accident and emergency departments "if absolutely necessary".
Blackpool Teaching Hospitals NHS Trust and the resort town's clinical commissioning group (CCG) warned of problems.
The CCG tweeted: "We are aware of an IT issue affecting some GP computer systems.
"Patients are asked for understanding whilst the issue is resolved.
"Please avoid contacting your GP practice unless absolutely necessary. Should you wish to obtain non-urgent medical advice, please call 111.
"Please also only attend the Walk-In Centre and A&E department if absolutely necessary."
A spokesman for NHS England said there was "an issue with IT", but referred further inquiries to NHS Digital, which did not immediately comment.
It comes months after Barts Health Trust, the largest NHS trust in England, was hit by a ransomware cyber attack.
The trust sent a message to staff urging them not to open email attachments from unknown senders.
Viruses such as ransomware are normally delivered via emails which trick the recipient into opening attachments and releasing malware onto their system in a technique known as phishing.
Derbyshire Community Health Services Trust tweeted: "We are aware of a major IT secure system attack.
"All IT systems have been temporarily shut down. More information will be available shortly."
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