Update: Microsoft's support account tweeted at 9.03am ET/14.03pm BST that Teams is now back online.
"We've monitored the environment and confirmed that the service is performing as expected," it tweeted. "If a user is still experiencing impact, they need to restart their clients to recover. Further details can be found under TM252802 in the admin center."
According to data from DownDetector, issues began at roughly 7am ET/12pm BST, preventing users from logging in or joining calls. Users in Europe and Asia were first to report issues, but the outage also affected Microsoft Teams customers on the East Coast of the US as well.
The Microsoft status portal reported no issues for Teams, so the source of the problems is still unclear.
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Global Teams outage
Soon after the outage began, the official @MicrosoftTeams account confirmed that "our team is investigating an issue with Microsoft Teams" and that the issue was global.
"We’ve confirmed that this issue affects users globally. We’re reviewing monitoring telemetry and recent changes to isolate the source of the issue. More information can be found under TM252802 in the admin center," an update tweet added.
Teams for Buiness, Teams Personal and Education users were all affected, with some users complaining they had been kicked out of active calls, and others suffering an Error 401 message.
This is the second major outage to hit Microsoft Teams in the last few weeks, with a similar issue in March 2021 linked to company-wide problems as the likes of Xbox Live, Office 365 and Azure also went down.
Microsoft said that outage was reportedly due to an issue concerning, "a recent change to an authentication system"
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Mike Moore is Deputy Editor at TechRadar Pro. He has worked as a B2B and B2C tech journalist for nearly a decade, including at one of the UK's leading national newspapers and fellow Future title ITProPortal, and when he's not keeping track of all the latest enterprise and workplace trends, can most likely be found watching, following or taking part in some kind of sport.