Social network Twitter is offline for many users, with web visitors being greeted by an error page.
Some mobile users are also unable to read or post tweets to the network, which has over 300 million active members.
Twitter chose to communicate the problem via a tweet, in which the firm said it was aware of the problem.
A spokesman for Twitter said that a tweet from the
The issue began shortly after 0800 GMT, according to Down Detector.
For some, the site appears to be intermittently accessible while the issue persists.