Microsoft is investigating an outage that has left thousands of users around the world unable to access the website's services, including Teams and Outlook.
It did not say how many were affected, but Downdetector.com which tracks outages through a range of sources including user reports, recorded thousands of people reporting problems with Teams, Outlook, Microsoft 365 and XBox Live.
It showed there were around 3,945 incidents of people reporting issues with email platform Outlook in the UK as of 7.43am today - and 1,461 with Teams.
Users in areas including Manchester, London, Birmingham, Norwich, Oxford, Brighton and Cardiff were reporting problems.
It also reported more than 3,900 incidents of people reporting issues with Microsoft Teams in India and over 900 in Japan.
Outage reports also spiked in Australia and the United Arab Emirates.
During the outage, most users were unable to exchange messages, join calls or use any features of the Team application.
Microsoft tweeted: "We're investigating issues impacting multiple Microsoft 365 services. More info can be found in the admin center under MO502273."
It later added: "We've identified a potential networking issue and are reviewing telemetry to determine the next troubleshooting steps."
Many users posted on social media to share updates, with #MicrosoftTeams trending as a hashtag on Twitter.
"Microsoft Teams and outlook are having issues here in Ethiopia… are these services down?" one social media user tweeted.
Another wrote: "Microsoft Outlook, Teams services down in Sri Lanka and around the globe."
Microsoft Teams is used by more than 280 million people globally and forms an integral part of daily operations for businesses and schools which use the service to make calls, schedule meetings and organise their workflow.
Microsoft Exchange Online, SharePoint Online and OneDrive for Business were also among the services affected, according to the company's status page.
The outage comes after Microsoft - which employs more than 220,000 people including 6,000 in the UK - last week announced plans for 10,000 job cuts across its global operations.
In a note to employees, chief executive Satya Nadella said the layoffs, affecting less than 5% of the workforce, were the result of a fall in investment amid fears the US and other key growth markets are heading for recession.