Twitter and Tweetdeck have gone down for some users after the social media giant suffered global outages.
"You might have had trouble Tweeting, getting notifications, or viewing DMs", the company said in a tweet on its Support account.
"We're currently working on a fix, and should be back to normal soon."
It did not give details about what caused the outage.
Outage monitoring website Outage.report received more than 4,000 reports of the incident globally, including Japan, Canada and India.
Meanwhile Downdetector's outage map shows that users worldwide are reporting problems, with those in the UK, Japan and West coast of the United States worst affected.
"Notifications aren't working, can't post any media, polls are blank (not showing up at all), news and trending is empty..." wrote one user on the Downdetector forum.
"Cant send new tweet on my TL. It's always 'you've already sent this tweet' - 'something went wrong' - 'some of your media failed to upload'," wrote another.
A Twitter representative had earlier told Reuters that the company was investigating issues with TweetDeck, which is used by reporters and other content creators for monitoring tweets from multiple Twitter accounts.
Log in attempts by users of TweetDeck seemed to be redirecting users to Twitter's website.
