Computers have been shut down across the country after NHS computers across the county were hit by a cyber attack.
A virus is understood to have targeted the health service network somewhere in Lancashire, a spokesman for Blackpool Clinical Commission Group (CCG) said, but has since spread.
Dr Tony Naughton, the chief clinical officer at Fylde and Wyre CCG, described the problem as 'national', while East and North Hertfordshire NHS Trust said it believed it had been hit by a 'cyber attack' and had suspended all non-urgent activity.
Tech experts are now battling to fix the problem, but computers at walk-in centres, hospitals, and at GP surgeries have been taken offline.
Patients have been urged to avoid them all 'unless absolutely necessary', and should call 111 for triage and medical advice.
GP and hospital appointments already arranged for this afternoon are still being held, it is understood, but new appointments cannot be made.
A spokeswoman for Blackpool Victoria Hospital pleaded for patients to only attend A&E in life-threatening emergencies, and asked for patience in other departments, which are running slower than usual.
"We are aware of an IT issue affecting some NHS computers systems," Blackpool CCG added. "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.
"Your local pharmacy can also provide free and fast advice for non-urgent conditions."
NHS Digital declined to comment immediately, but said it was preparing a statement.
One hospital worker said the virus is believed to be ransomware, which installs itself covertly on devices, and then holds information hostage until a ransom is paid.
More to follow