The full scale of the international cyber attack that continues to disrupt the NHS may only become apparent as people return to work today, experts have warned.

More than 200,000 victims in around 150 countries have been infected by the ransomware which originated in the UK and Spain on Friday before spreading globally.

Chinese state media reported on Monday morning that more than 29,000 institutions across the country have been infected, along with hundreds of thousands of devices, while companies in Japan were also hit.

Ciaran Martin, chief executive of the National Cyber Security Centre, said the outbreak could continue to infect more systems and other victims may emerge.

'We can't say what scale the new cases will occur at but it's likely there will be some,' he told the Press Association.

Around a fifth of NHS trusts were hit in the attack, forcing them to postpone operations and procedures over the weekend. The James Paget University Hospital in Gorleston was among those affected.

Dr Anne Rainsberry, NHS incident director, said: 'We have been working with 47 organisations providing urgent and emergency care who have been infected to varying degrees.

'Most have found ways of working around this but seven, including St Barts in London, have asked for extra support.'

It comes amid concerns networks were left vulnerable because they were still using outdated Windows XP software.

Brad Smith, Microsoft president and chief legal officer, described what happened as a 'powerful reminder' of the importance of updating software.

'The fact that so many computers remained vulnerable two months after the release of a patch illustrates this aspect,' he said in a blog post.

'As cybercriminals become more sophisticated, there is simply no way for customers to protect themselves against threats unless they update their systems.

'Otherwise they're literally fighting the problems of the present with tools from the past.'

Investigators from around the globe, including the National Crime Agency, are working to hunt down those responsible for the virus.

A British cyber whiz was hailed an 'accidental hero' after he registered a domain name that unexpectedly stopped the spread of the virus.

The anonymous specialist, known only as MalwareTech, issued a warning that hackers could upgrade the virus to remove the kill switch.