UPDATE: Google is reporting the issue experienced today as of 12:27 pm are now working as expected across all of their apps. Impacted apps as noted on their status dashboard included Gmail, Calendar, Drive, Docs, and Sheets.
Many Google Drive users are reporting access issues.
Google support has said that they are aware of the issue and have system maintenance going on right now to address it.
Depending on severity and numbers impacted they will update their apps status dashboard to both reflect the issue and their efforts at resolution.