Hackers have launched a co-ordinated cyber-attack on a number of NHS hospitals across the country
A number of sites appear to have been simultaneously hit by a bug in their computer systems.
In some cases emergency patients have been diverted to different hospitals.
NHS England said it was aware of the problem and would release more details soon.
Residents in some areas have been told to stay away from GP surgeries and A&E departements unless “absolutely necessary”.
St Barts Health NHS Trust, which runs The Royal London, St Bartholomew’s, Whipps Cross and Newham hospitals in London, said it had implemented its major incident plan to cope with disruption.
An NHS IT worker told the Guardian: “At approximately 12.30pm we experienced a problem with our email servers crashing. Following this a lot of our clinical systems and patient systems were reported to have gone down.
“A bitcoin virus pop-up message had been introduced on to the network asking users to pay $300 to be able to access their PCs.
“You cannot get past this screen. This followed with an internal major incident being declared and advised all trust staff to shut down all PCs in the trust and await further instructions.
“This is affecting the east of England and number of other trusts. This is the largest outage of this nature I’ve seen in the six years I’ve been employed with the NHS.”
Hackers installed virus pop-up messages demanding cash
An NHS Digital spokesman said: “At this stage we do not have any evidence that patient data has been accessed.
“We will continue to work with affected organisations to confirm this.”
He added the attack “was not specifically targeted at the NHS and is affecting organisations from across a range of sectors”.
The Health Service Journal said the attack had affected X-ray imaging systems, pathology test results, phone systems and patient administration systems.
NHS hospitals are diverting patients as a result of a cyber-attack in their computer systems
A doctor at one of the hospitals affected by the attack tweeted: “So our hospital is down. We got a message saying your computers are now under their control and pay a certain amount of money. And now everything is gone.”
A spokesman for East and North Hertfordshire NHS trust said: “The trust has experienced a major IT problem, believed to be caused by a cyber attack.
“Immediately on discovery of the problem, the trust acted to protect its IT systems by shutting them down..
Hackers are reported to have demanded cash from the NHS
“It also meant that the trust’s telephone system is not able to accept incoming calls.
“The trust is postponing all non-urgent activity for today and is asking people not to come to A&E – please ring NHS111 for urgent medical advice or 999 if it is a life-threatening emergency.
“To ensure that all back-up processes and procedures were put in place quickly, the trust declared a major internal incident to make sure that patients…