BlackBerry smartphone owners have been unable to browse the web, send e-mails or use the BlackBerry Messenger (BBM) service. Text messaging appears to have been unaffected.
In response, BlackBerry UK said that it knew about the problem - understood to have originated in a datacentre in Slough - and was "investigating".
In a tweet sent this afternoon, the company said: "Some users in EMEA are experiencing issues.
"We're investigating, and we apologise for any inconvenience."
A later statement said that BlackBerry was "working to resolve an issue currently impacting some BlackBerry subscribers in Europe, Middle East and Africa".
The first signs of problems emerged at around 11am UK time, but soon escalated as users took to Twitter to complain about the outage.
The Daily Telegraph reported a Twitter user named Amanda, from Twickenham, as tweeting: "So I have no email, Twitter or BBM on my BlackBerry. I may as well cut one of my arms off too *angry face*."
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