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.
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Twitter has been asked for comment.
The social network last suffered a major meltdown in mid-July, when accounts of high-profile users including former US President Barack Obama and Elon Musk were hacked, then used for posts about a bitcoin scam.
Twitter disabled all verified accounts as it grappled with that issue. A Florida teenager was arrested and faces charges in relation to the incident.
MORE TO COME