Many users of the micro-blogging site were unable to access any of its pages for a couple of hours.
Its status page read: "Users may be experiencing issues accessing Twitter. Our engineers are currently working to resolve the issue."
It is currently unclear why the site went down, but it was brought back online soon after its first status message.
The front page of Twitter for a short time had the greeting: "Twitter is currently down for <%= reason %>.
"We expect to be back in <%= deadline %>. For more information, check out Twitter Status. Thanks for your patience!"
Google Talk also experienced a power outage earlier today, but most of its service has now been restored.
Twitter recently denied reports that it was hacked when it experienced an outage on June 21.