A number of leading websites including Amazon, Reddit and Twitch are currently not working.
According to the BBC, the UK government website – gov.uk – is also down as is parts of the 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.