Microsoft has said its service has been fully restored after a massive outage that saw widespread disruption to governments, businesses and public services around the world.

The technology company said on Saturday morning it had restored service to the remaining customers affected by one of the worst IT failures in years. On its Microsoft 365 status page, the US-based firm said: “We have completed our efforts to address the underlying issue of the incident and restored service to the remaining impacted customers and regions.

“Further updates can be found at MO1550821 in the Microsoft 365 admin center.”

The outage, which began on Thursday, affected governments, courts, healthcare services, businesses, airlines and banks. Governments including those of Japan, Singapore and Australia reported that the hours-long episode had affected some of their operations.

View image in fullscreen People pass Microsoft’s offices in Tokyo, Japan on Friday. Photograph: Andrew Caballero-Reynolds/AFP/Getty Images

In the UK, where NHS England has a five-year deal to use Microsoft 365, vital public services were hit, with hospital staff resorting to paper records and one union reporting that ambulance services had suffered a “serious impact”.

The already backlogged court system was also hit, with juries in some cases being sent home early or prisoners not being sent to court, while at Minshull Street crown court in Manchester staff scrambled to locate a fax machine.

In the US, school districts told parents they must reach out by phone or online apps to contact their child’s school, while staffers at the House of Representatives told Politico they had lost a day of work.

One detention facility in Colorado said they were unable to take online bond payments to release detainees and told anyone needing to post bond for immediate release to do so in person at the jail.

In Australia, many people who rely on Microsoft 365 reported being unable to access their inboxes, including at councils, courts and schools. The federal police and Asio, Australia’s national domestic security and intelligence agency, were also affected by the outage.

Asio’s director general, Mike Burgess, said the agency’s systems “operate on multiple levels”, adding that they had been affected “on one level, yes, but not completely”.

Across Europe, government agencies in the Netherlands, Belgium and France reported problems, with a French municipality instructing citizens to use the phone instead of emailing.

In Japan, government email services became unavailable and staff resorted to text messaging. The shipping firm Sagawa Express was unable to accept some online reservations while Taisho, a major pharmaceutical company, said it was having to handle orders by phone.

The Indian airlines IndiGo and Akasa Air said their email support services were affected, and Taiwanese security firms, life insurers and investment trust companies told Reuters that fund management services had been disrupted.

Users reported that Microsoft 365 services, including Outlook, Teams and the AI assistant Copilot, were interrupted. Downdetector, an online tracker, said it received outage reports from users in more than 70 countries and territories.

Approximately 430 million people use Microsoft 365 apps, Microsoft said on its website. Problems began at about midday on Thursday in the US and at 6pm in the UK.

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The Washington-based company apologised on Friday for the disruptions and said the outage was “not related to cyber” or artificial intelligence agents. It said the incident “was introduced by an issue during an earlier network capacity upgrade that surfaced” after a recent network change.

The disruptions offer the latest example of the cascading problems that can erupt when multiple communications and technology platforms depend on the same provider. The outage has fuelled concerns in the UK about an overreliance on a small number of tech companies.

Steven Murdoch, a professor of security engineering at University College London, told the Guardian an outage of this size was usually “the result of some surprising interaction between systems. Each of the systems is normally quite well understood but interactions between them are complex and frequently the cause of large outages like this.

“It’s very hard to build a complex system without there being some risk of some failure.”

Tim Clement-Jones, a former chair of the House of Lords artificial intelligence select committee, said the widespread outages of vital government services were an “I-told-you-so moment” highlighting Britain’s dependence on US tech.

Jeremy Singer, a professor at the University of Glasgow’s School of Computing Science, said: “This problem serves to emphasise the dependence we have built on one company’s digital infrastructure, and may lead us to question whether we need more resilience in our IT ecosystem.”

The total number of people affected was not clear, but Microsoft said in January it had more than 450m paid commercial subscriptions to its 365 services.