Gamers trying to log onto Xbox Live were met with the message: "There was a problem. We couldn't sign you in. Try again in a few minutes, or check your account by signing into account live"
The problems are affecting users on Xbox One, Xbox 360, Xbox on Windows 10 and other Xbox devices.
According to website DownDetector, which tracks major network outages, problems started at around 17:26 GMT.
"Our engineers and developers are actively continuing to work to resolve the issue causing some members to have problems finding previously-purchased content or purchasing new content," said Xbox in a statement on its Live Status page, which shows the status as "Limited".
"Stay tuned, and thanks for your patience."
Xbox Live is a paid-for subscription service that allows gamers to play multiplayer games online as well as buy and download titles.
It's unclear at this point what has caused the outage. There's a possibility it is just a connection problem or it could be the result of a deliberate cyber attack.
Xbox Live users are currently having trouble accessing major parts of the service, including signing in and buying items, according to anecdotal reports and Microsoft’s own status page.
As of 1:43 p.m. ET today, Microsoft’s status page mentions “limited” access to Xbox Live “core services” — including sign-in, creating or recovering an account, and search — as well as making purchases, redeeming codes and downloading items. The problems are affecting all platforms: Xbox 360, Xbox One, Xbox on Windows 10 and Xbox on devices such as smartphones.
The launch day for any major game is a bad time for an online gaming service to go down, and it’s possible that Microsoft is dealing with an increased server load due to the arrival of Mass Effect: Andromeda today.
“Our engineers and developers are actively continuing to work to resolve the issue causing some members to have problems finding previously-purchased content or purchasing new content,” reads a note on the status page. At least one member of Polygon staff is currently unable to sign into his Xbox Live account on his Xbox One or on the Xbox website.
We’ll keep you updated as Microsoft provides further details on progress with its fixes.
Update: The issues aren’t limited to Xbox. The Verge reports that Microsoft Account users are experiencing “widespread issues” across multiple services, including Outlook, Skype, OneDrive and the Windows Store.
Update 2 (5:37 p.m. ET): Microsoft gave the all-clear on the Xbox Support Twitter account a short while ago.