More than 75,000 similar attacks reportedly happened in nearly 100 countries, with Russia, Ukraine and Taiwan hardest hit, according to the cybersecurity firm Avast.
The cyberattack, in which harmful software took over computers, encrypted the information and then demanded payment of $300 or more from users before releasing the devices, affected some of the world's largest institutions and government agencies, including the Russian interior ministry, FedEx in the United States and Britain's National Health Service.
"Computer systems which are not updated are vulnerable to such attacks". Patients were asked not to come to hospitals unless it was an emergency.
The attack is believed to be the first in which such a cyberweapon developed by the NSA has been used by cybercriminals against computer users around the globe.
"The NHS was not particularly targeted".
Of 248 NHS organizations, 48 were affected by the attack but "most of them are back to the normal course of business", the Press Association reported British Home Secretary Amber Rudd as saying.
An worldwide effort is under way to track down the criminals behind an unprecedented global cyber attack that wreaked havoc across the NHS in England.
The so-called ransomware has wormed its way into thousands of computer systems in an apparent extortion plot, shutting users out unless they coughed up a payment.
Pictures on social media showed screens of NHS computers with images demanding payment of $300 (230 pounds, 275 euros) in Bitcoin, saying: "Ooops, your files have been encrypted!"
He said the affected computers likely had not applied the Microsoft patch or were running old operating systems for which no patch was available.
The head of Turkey's Information and Communication Technologies Authority or BTK says the nation was among those affected by the ransomware attack.
Faria Hossain, a joint news editor of the channel, said around 8:00pm she found the notice on her computer and after that she could not work on it.
Wainwright said Europol was working with the Federal Bureau of Investigation in the United States to track down those responsible, saying that more than one person was likely behind it.
CERT Chief Information Security Engineer Roshan Chandragupta said they were attempting to figure out how the attack was being spread.
NHS England said patients needing emergency treatment should go to Accidents and Emergency or access emergency services as they normally would. Windows machines that are up-to-date are safe from this ransomware.
Although Nissan said it is "working to resolve the issue", it remains to be known whether the ransomware attack, a type of software which takes over files until the company pays a ransom, has actually impacted production at the Japanese auto giant.
An Indian-origin doctor based in London had warned against the cyber-hack of the UK's state-run National Health Service (NHS) just days before it crippled the country's network.
Elsewhere in Europe, the attack also hit companies including Spain's Telefonica, a global broadband and telecommunications company.
In statement, the Trust said: "We are continuing to deal with a major IT disruption and we are sorry for any delays experienced at our hospitals".
Routine appointments had been canceled and ambulances were being diverted to neighboring hospitals.
Griffiths, who was receiving chemotherapy at Bart's, said several cancer patients had to be sent home from Bart's because their records or bloodwork couldn't be accessed.
The central bank's IT attack monitoring centre "detected mass distribution of harmful software" but no "instances of compromise", it said.
Meanwhile, a global manhunt is on for the perpetrators of the attack that is being described as the biggest-ever cyber ransom attack.
Security experts said the attack appeared to be caused by a self-replicating piece of software that enters companies when employees click on email attachments, then spreads quickly internally from computer to computer when employees share documents.