A number of major websites have been hit in a massive and simultaneous internet outage.
Amazon, the BBC and the UK government's sites were among those affected on Tuesday morning.
Leading media websites including the Guardian, Financial Times, Independent, New York Times, Evening Standard and Reddit were also among those giving error messages.
The outage meant some websites went down completely, while others experienced smaller disruption and were still able to operate.
Some of those that initially went down, including the UK government's and BBC's, gradually returned to service.
Tech experts said there is no evidence the outage was caused by malicious activity.
Instead, it appeared to have been sparked by an issue with Fastly, one of the world's major content delivery networks (CDNs).
A CDN is a system used to host websites and their content on the internet and serve it to users. Fastly reported a major outage across its global network, which is believed to have caused the outage.
The company offers services such as speeding up loading times for websites, protecting them from denial-of-service cyberattacks and helping them deal with bursts of traffic in order to stay online and stable.
The US firm confirmed it was “currently investigating potential impact to performance with our CDN services”.
It later said: "The issue has been identified and a fix has been applied. Customers may experience increased origin load as global services return."
Alex Hern, the Guardian’s technology editor, tweeted that Fastly had "been identified as the cause of the problem”.
“The outage, which began shortly before 11am UK time, saw visitors to a vast array of sites receive error messages including ‘Error 503 Service Unavailable’ and a terse ‘connection failure’."
The official gov.uk Twitter account said: “We are aware of the issues with http://gov.uk which means that users may not be able to access the site. This is a wider issue affecting a number of other non-government sites. We are investigating this as a matter of urgency.”