A number of leading websites are currently not working, including Amazon, Reddit and Twitch.
The UK government website – gov.uk – is also down as is parts of the media giant BBC and a host of other media outlets.
Affected websites displayed the message: “Error 503 Service Unavailable”.
Early reports suggested it could be related to Fastly, a cloud computing provider, which underpins a lot of major websites.
Fastly said it was investigating problems with its content delivery network.