Microsoft is currently looking into an authentication error hitting its Office 365 systems.
"Starting at approximately 21:25 UTC, a subset of customers in the Azure Public and Azure Government cloud may encounter errors performing authentication operations for a number of Microsoft/Azure services, including access to the Azure Portals," the company said in a status post.
In another post, the company said users would be unable to access Office.com, Outlook.com, Teams, Power Platform, and Dynamics365.
"Existing customer sessions are not impacted and any user who is logged in to an existing session would be able to continue their sessions," Microsoft said.
On its Twitter status account, Microsoft said the root cause appeared to be a recent change, and that it had decided to roll the change back.
"We've rolled back the change that is likely the source of impact and are monitoring the environment to validate that service is recovering," the company said, before following up 14 minutes later to say it was not seeing what it expected to see.
"We're not observing an increase in successful connections after rolling back a recent change. We're working to evaluate additional mitigation solutions while we investigate the root cause."
By 00:40 UTC, Microsoft said it was seeing improvement across multiple services.
"We're continuing to see significant improvement for affected services and most users should be experiencing relief," Microsoft added at 1:20 UTC.
At 4:00 UTC, the company said the issue was resolved.
"We've confirmed that the residual issue has been addressed and the incident has been resolved. Any users still experiencing impact should be mitigated shortly," it said.
Updated at 11:31am AEST, 29 September 2020: Added further Microsoft updates.
Updated at 2:06pm AEST, 29 September 2020: Issue resolved. Changed headline to reflect new status.