A cyber-attack on the NHS is affecting hospitals and GP surgeries across England and in Scotland
Ransomware software that locks computers, demanding payment, is being seen on screens
Theresa May says the NHS incident is part of a wider cyber-attack affecting organisations around the world
Similar infections are reported by Spanish utility firms, and in the US, China, Russia, Italy, Vietnam and Taiwan
Up to 28 NHS organisations in England are said to have been affected, as well as five GP surgeries in Scotland
GPs reported to be using pen and paper in some areas
Some hospitals are diverting patients
An anonymous update from Cumbria:
Cumbria Community NHS trust is also affected by the cyber attack. All their systems are down.
The district nurse visiting us today said they can't access any of the notes or even print of the list of addresses they have to visit.
Image source, Emma FardonDr Emma Fardon, a GP in Dundee, told the BBC:
"It became very obvious at around 1pm. I came back from house visits to find all our computers hit by the virus.
"It was the red display asking for the money. We can’t access any patient records.
"Everything is fully computerised. We have no idea what drugs people are on or the allergies they have. We can’t access the appointments system.
"We’ve had to try and phone as many people to rearrange their appointments to next week.
"It’s had a massively disruptive effect. We can’t process any documents, can’t issue prescriptions, or look up results.
"We’re trying to accommodate who we can. We are still seeing people who really need it.
"We’ve had glitches in the past but I’ve never seen anything as bad as this. We’ve no idea how long it will last for."
A parent tells us: Northumbria trust hospitals are also affected. My son had an accident at school today. We have to go back to Hexham hospital tomorrow for an X-ray as all systems were down.
NHS sources tell the BBC that the prevention patch for this particular malware can be quickly installed. But once systems are affected, there is no indication, as yet, on how long it will takes to fix them.
Dr Tarek Seda says he had to divert a serious case because of the "cowards" behind the NHS cyber attack.
Although not all NHS trusts have been affected by the cyber-attack, hospitals say protecting patient information is a "top priority".
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Saffron Cordery from NHS Providers tells the BBC she believes around 21 hospital trusts are now affected.
She added that GP practices, pharmacies and universities had also been affected.
But she said that, despite the major incident, anyone who turned up at an A&E in an emergency situation would be given first-class treatment.
An anonymous doctor writes:
"York, Grimsby, Bassetlaw are all affected. One doctor describes a matron running around the wards yelling at everyone to turn off their computers."
A GP in York tweets asking patients to bear with their doctor after the cyber-attack affecting NHS Digital. At least that's the spelling we're assuming is intended.
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The cyber-attack in Spain - similar but not yet linked to the one on the NHS in England - appears to have targeted utility firms.
Power firm Iberdrola and utility provider Gas Natural have reported problems, as well as telecoms giant Telefonica.
Adam Jinkerson
BBC Local Live
Dr Mils Hills, who is an associate professor of risk, resilience and corporate security at the University of Northampton, has told the BBC the cyber attack on the NHS "could have been prevented".
"It's most certainly going to have come from a user clicking something they shouldn't have, whether it's in an email or on an internet browser tab," he said.
"Hospitals should have measures to prevent this.
"It will be fixed and removed, but it will cost a lot. The task to fix it won't be difficult, but will be time-consuming.
"The problem is this is a pretty low-level attack and it's causing such chaos."
An NHS Digital statement said: "NHS Digital is working closely with the National Cyber Security Centre, the Department of Health and NHS England to support affected organisations and ensure patient safety is protected."
A spokesman for Hull and East Yorkshire Hospitals NHS Trust, confirmed malware was detected on their systems but it had "not had a significant impact".
He added: "Our IT team responded rapidly and we have blocked all incoming email and all web mail for the time being. No patient systems are affected."
BBC Radio 4 presenter Matthew Price explains why cyber-attackers would potentially want to target the NHS.
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Health Service Journal correspondent tweets...
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Robert Schifreen explains how attacks like the one on NHS services spread.
Read MoreDetails from Spain's National Cryptology Centre on which computer systems are being affected:
As well as those in the UK and Spain, there are also reports of mass computer infections in Italy, Portugal, Russia, Vietnam, Kazakhstan and Taiwan.
It is not yet clear whether the attacks are all connected.
One cyber-security researcher tweeted, external that he had detected 36,000 instances of the ransomware, called WannaCry and variants of that name.
Prime Minister Theresa May is being kept informed of the situation involving the NHS cyber-attack, a Downing Street spokesman says.
Health Secretary Jeremy Hunt is currently being briefed by the National Cyber Security Centre.
Carl Buckley from South Shields, Tyne & Wear, tells us:
“I went to my GP’s this afternoon to collect a repeat prescription.
“While I was there I asked about the results of an X-ray I was also waiting on.
”The receptionist started to look on the computer and after a few minutes of her trying to find the details told me the system wasn’t working.
“She asked me to wait while they rebooted it.
“20 minutes later they told me it wasn’t working and suggested the computers were down across the NHS
“I told them I had read about the cyber attack.
“Patients were arriving at the surgery and the automated appointments system wasn’t working either so it was quite chaotic”
Kevin who works in the A&E department at the University Hospital in Coventry and Warwickshire emailed the BBC to say: "The computers are down so we can't register people arriving.
"The queue, currently 17 people and growing, is almost out the door!"