Twitter said on its status website that it was investigating an "unresolved incident" caused by irregularities found in Twitter's application programming interfaces. "We are now investigating this issue".
Twitter said that the issue was caused by "an inadvertent change we made to our internal systems".
The move ignited claims that the platform was biased against conservatives.
Report Door staffers are seeing the outage across the United States and in the UK, though we have been able to send a few DMs through the platform.
Twitter in a statement said that its micro-blogging platform was down for many users earlier in the day due to some trouble with its internal systems.
Twitter CEO Jack Dorsey tweeted on Wednesday, "Our communications about our actions on the nypost article weren't great".
At around 2340 GMT, it was possible to carry out certain functions, such as retweeting a post, but many users were still unable to send a new tweet.
Twitter down, suffers worldwide outage
The unexplained outage began at around 10:30 p.m. Thursday, according to data from Downdetector.
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 now investigating this issue".
"We are continuing to monitor as our teams investigate".
Soon after the company announced that the issue has been fixed for most users and others should also get back to the service soon. "If you disconnected at all, a Replay will recover any Tweets during your disconnect, and the volume is likely to be very small".
In response to the hack, Twitter temporarily prevented all verified accounts with blue ticks from uploading tweets as it carried out an investigation.
Thursday's outage was the latest technical breakdown to knock Twitter offline.
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