Mass General Brigham - one of the biggest healthcare systems in America - has axed all non-urgent visits, procedures and surgeries amid a global IT failure.

Hospitals were thrown into chaos overnight when the outage took out Windows systems around the world, knocking computers and medical devices offline and forcing medical staff to revert to pen and paper.

Mass General Brigham in Boston - which sees 2.5million patients a year in its 15 hospitals and clinics - said it would only provide care to patients who have urgent health problems. 

Tufts Medical Center and South Shore Health, also in Boston, were also experiencing issues linked to the global tech outage. 

But the issue extends well beyond Massachusetts. Hundreds of hospitals are thought to be impacted by the issue.

Frightened healthcare staff and patients in hospitals across the United States are documenting the chaos inside the facilities caused by a major worldwide IT outage on social media. 

'We have dedicated every available resource to resolve this issue as quickly as possible, and we apologize for the inconvenience this has caused our patients,' Mass General Brigham said.

'It is our highest priority to ensure that our patients receive the safest care possible.' 

A spokesperson added: 'We continue to care for all patients currently receiving care in our hospitals.' 

In New York, The Mount Sinai Health System, which operates seven major hospitals in New York City and Long Island, as well as dozens of specialty and out patient clinics across the five boroughs, has seen its computer systems go down because of the outage. 

Workers throughout the institution, which is ranked as one of the best in the country, have had to move to pen and paper medical charting.  

Employees at Cornell in New York also said some of their systems went down. 

NewYork-Presbyterian, which oversees Weill Cornell Medicine and Columbia in New York, said its hospitals have not been 'directly impacted' by the outage and its hospitals are continuing to operate normally. 

The system is also working with its partner healthcare facilities to 'assess the impact to their outpatient services.' 

Penn Medicine, which has eight hospitals across Pennsylvania and New Jersey, is experiencing an outage of its systems and has had to delay non-emergent surgeries, as well as revert to handwritten charts. 

Cincinnati Children's Hospital told ABC News patients may continue to arrive for surgery or appointments but should be prepared to experience delays.

All non-surgical and office appointments were canceled before 10 am. 

Martha's Vineyard Hospital said it had canceled non-emergent operations and medical appointments.  

Other hospital systems affected include Cleveland Clinic, Kaleida Health/Cayuga in Buffalo, Harris Health System in Texas, the Hospital for Special Surgery in New York City, Memorial Hermann in Texas, Nationwide Children's Hospital in Ohio and Ohio State University Wexner Medical Center. 

Healthcare workers say Epic, a major medical software program, is non operational and causing the disruption in accessing patient charts. 

Epic is used in hospitals across the world. According to the company, more than 305million patients have a current electronic record in Epic.

And in 2022, it held medical records of 78 percent of patients in the United States and more than three percent of patients worldwide.

Without access to patient's digital charts, healthcare providers cannot see medical history or previous medications given, putting patients at risk of major complications. 

Additionally, patients may experience issues with trying to access any of their own electronic medical records.  

The outage is believed to be from a software update from a cybersecurity company called CrowdStrike, a tool is used to protect against hacking threats, and is not believed to be linked to a malicious cyberattack. 

While paper charts were once the norm in healthcare, the advent of technology in the medical field made them obsolete and nearly all day-to-day operations are conducted via computer programs.  

The full impact of the bug is not known yet, but hundreds of thousands of computers around the world suddenly shut down in the early hours of Friday, impacting businesses, transport links and TV broadcasts globally.

The issue seemed to impact PCs running on Microsoft’s Windows 10.

In one TikTok video, a woman in a breathing mask suggested her electronic medical records could not be accessed, leaving her unable to get the correct meds.

In another, staff can be heard shouting with panicked voices as the camera pans to a computer that has been knocked offline and is showing a so-called 'screen of death.'

Meanwhile a nurse in Orange County, California detailed how staff have had to revert to pen and paper and using iPhones to treat patients and prescribe drugs, raising the risk of errors.

The provider said Epic 'self-deleting' off of Microsoft computers whenever they are restarted, and as quickly as they turn on, the computers go 'back down.'

Also thrown into chaos were 911 and non-emergency call centers, which are not working correctly across multiple states.

While it has not been attributed to a cyberattack or hack, in previous instances when hospital computer systems have gone down, patients previously DailyMail.com they were denied medications for blood clots, addiction, and cancer or had to pay as much as seven times the normal cost after insurance.

And in one case, a nine-month-old baby lost her life.

Experts at the Ponemon Institute, an independent research group that studies critical security issues, surveyed more than 600 healthcare facilities, finding mortality rates increased at a quarter of locations following a ransomware attack. 

This is a developing story