Microsoft 365, Outlook and Teams have all been affected.
There were more than 97,000 incidents of people reporting issues with Outlook, according to Downdetector, which tracks outages by collating status reports from a number of sources. The actual number of affected users may vary.
Downdetector also recorded more than 38,000 user reports of problems with Microsoft 365 and about 4,500 reports of users having trouble accessing Teams.
"We're aggressively pursuing all pathways to reduce impact," Microsoft said in a statement.
Its team has paused all deployments, is moving additional traffic off the affected infrastructure, and is restarting affected servers to return them to service, the company added.
Microsoft said earlier in the day it had fixed a Teams disruption affecting users in North America and that the impact had been fully resolved. The company later said the issue may also affect Microsoft 365 service connectivity for users in other regions.
OpenAI said it was investigating an issue with Microsoft connectors in which new connections may be broken and tools are not working as expected.
Anthropic said it had identified an issue with an upstream provider affecting its Microsoft 365 connector.
