Microsoft Corp said Office 365, Teams and some of its other online services are experiencing service interruptions.
A company spokesman confirmed the outages, which are also impacting Exchange Online and OneDrive.
He didn't have any information on the reason or the time it will take to get the services up and running again.
Problems with some of these services were reported earlier on Monday (Sept 28) by Downdetector, which aggregates user reports of issues. That suggests the outages have lasted at least two hours.
Office 365 packages popular Microsoft software such as Word, PowerPoint and Excel into an online subscription. Teams is a collaboration tool that integrates with Office 365.
The disruption follows a similar incident the previous week when some users of Google's G Suite cloud productivity tools experienced errors.
The outages may be more disruptive at the moment because so several people are working and studying remotely.
Microsoft and Google's offerings are used widely by schools and other educational organizations, which are conducting most classes over the internet.