While not yet reflected on Apple's system status page, a number of Apple services are currently experiencing downtime or slow performance, including the App Store, Apple Music, iCloud, and the iTunes Store. Apple's website is also experiencing some issues, including its developer portal being unavailable right now.
The issues span multiple countries and extend to Apple's Mail and TV apps. Not every user is affected, so your mileage may vary as Apple works through its server issues. We'll update as the situation unfolds.
Update - 10:45 a.m. Pacific Time: Apple's services and developer portal appear to be functional again.