Twitter is suffering widespread outages that began around 10.30am NZT.
Users in the US, UK and NZ have reported not being able to access the social network or that it does not refresh - and the outage tracker Downdector.com has seen a massive spike in complaints about Twitter.
A brief message on Twitter's status site, posted at 10.56am NZT, says there is an "irregularity with Twitter APIs" (application programming interfaces) and that "We are currently investigating this issue. More updates to come."
Some users are still able to send direct messages.
Twitter has been asked for comment.