The service had been down for users around the world, showing 404 pages and error messages instead of important meeting and event information. Problems started to crop up early in the morning, and Google tweeted that it was "experiencing a service disruption."
Google didn't immediately have a comment on what caused the problem.
A message, posted to the G Suite Status Dashboard at 7:22 a.m. PT, said the company was investigating reports of issues with Google Calendar and that affected users were unable to access the service. Google said that "system reliability is a top priority."
Users reported trouble opening Google Calendar on desktop as well as mobile devices. However, the Google Calendar app for iOS and Android appeared to remain working.
Without knowing what meetings, classes and other events were scheduled for the day, some took to social media to share their frustration. Google Calendar and the hashtag #googlecalendardown were trending on Twitter.
"So do we get bonus points if we show up to meetings without the help of Google Calendar? #404meetingnotfound" wrote one Twitter user.
"When google calendar goes down, is it like the purge but for meetings?" wrote another Twitter user on Tuesday.
"As part of Google's "Don't Be Evil" strategy they've deleted Google Calendar, you no longer have to attend meetings," wrote another Twitter user.
Originally published June 18, 7:44 a.m. PT.
Updates, 8:23 a.m.: Adds more reactions and response from Google. 9:14 a.m.: Adds more details. 11:20 a.m.: Notes that Google Calendar is back up.