An unknown problem is causing difficulties with very many of Apple's iCloud services and is also affecting retail stores which are reportedly unable to complete sales. Update: Apple has now restored many of the 21 services.
The problem appeared to be quickly worsening, too, as more services were being affected. That appears to have stemmed and Apple has been reporting mostly steadily improved services all round. After approximately 90 minutes, an Apple Pay issue regarding the ability to use or suspend cards was the first to be fixed.
Game Center and iCloud Mail problems were next to be fixed. Apple's automated system status has been reporting fluctuating numbers of resolved issues, but currently it claims 18 out of the 21 issues had been fixed.
The remaining services still having difficulties include iCloud Reminders and iCloud Calendar.
iCloud is down in case you haven't lost your mind trying to enter your password already— meaningful internet moniker (@loudersoft) July 4, 2019
Apple has yet to comment but customers on Twitter were reporting similar failures in Apple Stores. Reportedly some number of transactions are failing to complete, presumably because of the same issue.
This incident appears to have been more widespread than previous iCloud problems, but the service has been affected before, as recently as June where two separate incidents cause issues with the iTunes Store and basic iCloud functions.
Update: 2:33 p.m. EDT Apple resolved the Apple Pay issue.
Update: 2:47 p.m. EDT Apple fixes iCloud Mail and Game Center problems.
Update: 3:00 p.m. EDT Apple claims 18 services restored.
Update: 5:32 p.m. EDT All issues have been resolved.