The site appears to have stopped responding, at about 11.30am UK time.
The new outage follows a morning where Twitter — including the website, mobile apps and TweetDeck — were all offline. They came back up again at around 10am, but appear to have gone offline again.
Unlike the earlier outage, the Twitter site wasn't accessible at all, only loading a blank page. The first time, Twitter had shown a little robot and a message that something was "technically wrong".
The first time Twitter went down, its @Support account tweeted that "Some users are currently experiencing problems accessing Twitter. We are aware of the issue and are working towards a resolution". (That account is itself part of the outage, but Twitter sent the text of the tweet to The Independent.)
Twitter's status page was updated to reflect the earlier outage this morning. The site did not say then that the problem had been fixed, and so it is likely that the new outage is linked to the old one.