Apple has confirmed several of its main services - including iTunes and the App Store - are currently unavailable for some users.
According to the tech giant's website, the ongoing technical difficulties began shortly after 2.30pm UK time on Tuesday afternoon.
In a statement, it said: "We are investigating and will update the status as more information becomes available."
At least 12 of the company's services are disrupted - including the iBooks Store, Apple TV, OS X Software Update, and the recently launched Apple Music.
The fault came as Apple's Beats 1 radio station, which opened last month, exclusively announced the nominees for the MTV Video Music Awards. Its tagline is "worldwide, always on".
Taylor Swift leads the VMAs with nine nominations - with her star-studded music video for Bad Blood being shortlisted in seven categories. Another of her hits, Blank Space, received nods in two categories.
Ed Sheeran has six nominations - and both stars are joined in the Video of the Year category by Lamar, Beyonce and Mark Ronson.
Multiple regions appear to be affected by the glitch - with users in Asia, Europe and the Americas all experiencing issues.
Apple, which will be reporting its third-quarter financial results later this evening, has not made any further comment about the outage.
The company was forced to make a significant U-turn when launching Apple Music, after Taylor Swift criticised how artists would not receive royalties for songs played during a three-month free trial period for the streaming service.
Describing Apple's decision as "shocking" and "disappointing", the 25-year-old had posted on Tumblr: "We don't ask you for free iPhones. Please don't ask us to provide you with our music for no compensation. To Apple, Love Taylor."
Soon afterwards, one of Apple's senior executives, tweeted: "Apple will always make sure that artists are paid. Apple Music will pay artist for streaming, even during customer's free trial period. We hear you taylorswift13 and indie artists. Love, Apple."