Twitter says it has reversed a software update that led to outages reported across Europe, the Middle East, Africa and North America that affected users on computers and phones.
Both Twitter's web and mobile services began suffering outages concentrated in northern Europe around 8.20am, 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 2.20pm, six hours after they first began to spread.
At approximately 5.45pm Twitter reported that some users were still having trouble accessing the service.
"We are aware of the issue and are working towards a resolution," a statement on the company's Twitter status website said.
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.
Twitter's shares were down more than 7% when markets closed