Thousands of incidents were logged by the tracking website Downdetector, with complaints spiking in the hour from 0700 GMT and particularly affecting users in Asia and Europe.
“We’ve isolated the problem to a networking configuration issue, and we are analyzing the best mitigation strategy to address it without causing additional impact,” the firm said in an update at 0900 GMT.
Microsoft did not reveal how many users were affected and did not respond to AFP requests for comment.
But its update said the issues were causing problems in several apps on the Microsoft 365 online office suite, which has more than 300 million users.
Teams, a messaging programme for companies, and email client Outlook are among the most widely used.
Thousands were taking to social media to register dismay at the technical problems.
“I have a paper in half an hour on MS teams and the servers are not working in India,” said one Twitter user, adding: “Please do something.”
Earlier this month, the firm announced it would be cutting 10,000 staff, almost five percent of its global workforce.