Microsoft Office 365 users have taken to Twitter to complain that the company's services are down.
Users in the US, Australia and New Zealand have been badly hit, according to outage tracker website Downdetector.
Microsoft 365 said in a Twitter post it was investigating the issue.
"We've identified that multiple Microsoft 365 services are affected and we're actively looking for the swiftest means of restoring access."
Some Twitter users have reported the issue has been resolved while others say they're still offline.
"Wish you guys would make your details available more openly," one user wrote.
Released in 2011, Office 365 is an integrated product of Microsoft apps and services.
Products in the service include Outlook 365 and Skype.