Several of Apple's services are experiencing an outage at the current time, with Apple noting service interrupts for iCloud Backup, iCloud Drive, iCloud Notes, iCloud Storage Upgrades, and Photos on its System Status page.
The issue has been ongoing since approximately 10:13 a.m. Pacific Time. Apple says that users may be unable to use these services during the outage, so features like iCloud Backup and iCloud photo storage may not be working at this time.
There's no word on when these problems will be resolved, but we'll update this article when everything is back up and running. Earlier today, services like the App Store, Apple Music, and iTunes Store, also saw an outage that has since been addressed.
Update: The problem has also expanded to iCloud Storage, Calendar, Mail, Keychain, and Bookmarks.
Source: Macrumors