Twitter said on Tuesday its social network was suffering ongoing outages on computers and phones and it was working to resolve issues which have been widely reported across Europe, the Middle East, Africa and North America.
Both Twitter's web and mobile services began suffering outages concentrated in northern Europe around 0820 GMT, with smartphone users receiving the warning: "Tweets aren't loading right now."
Users from Scandinavia to Saudi Arabia to South Africa reported outages. India and Russia also suffered performance issues, according to a Twitter technical site.
Intermittent breakdowns later spread to the United States and Canada in the early part of their working day.
Sporadic disruptions continued at 1420 GMT, six hours after they first began to spread.
"Some users are currently experiencing problems accessing Twitter," a statement on the company's Twitter status website has read for several hours (status.twitter.com/).
"We are aware of the issue and are working towards a resolution." A company spokeswoman had no further comment.
Services had been restored for some affected users, only to fail again later. Some Twitter features continued to operate normally for some users, while others suffered disruptions, according to Twitter's developer website.
The on-again, off-again nature of the outages meant that the hashtag #twitterdown was trending as a topic while Twitter was down for many other users.