According to a post on Twitter's official blog for status updates, the company was aware of problems affecting its network from around 4 a.m., Eastern time. The website Down Detector, which tracks reports of outages for various sites, backs up that timeline.
Many news organizations across the globe reported on the outage. As of 8 a.m., some organizations (and Twitter users themselves) said that service was being restored, though some were still reporting technical problems.
The company did not say how many of its 320 million active users were affected by the outage.
While Twitter had a reputation for outages in its early days (its "fail whale" was a familiar sight), the company has taken great pains to stabilize its service as it has grown. According to the company's blog, however, it had a brief 10-minute outage on Monday, as well as a roughly 20-minute disruption on Friday.