The UK government website - gov.uk - was also down as were the Financial Times, the Guardian and the New York Times.
Cloud computing provider Fastly, which underpins a lot of websites, said it was behind the problems.
The firm said there had been issues with its global content delivery network (CDN) which it was fixing.
In a statement, it said: "We identified a service configuration that triggered disruption across our POPs (points of presence) globally and have disabled that configuration.
A POP allows content to be sent from globally distributed servers that are close to the end user.
"Our global network is coming back online."
The issues began at around 11:00 BST and lasted for an hour. Other affected websites included CNN and streaming sites Twitch and Hulu. The outage also broke some parts of other services, including Twitter's emojis.
Websites were also beginning to be restored, after around an hour of downtime.
Fastly runs what is known as an "edge cloud", which is designed to speed up loading times for websites, as well as protect them from denial-of-service attacks and help them when traffic is peaking.
It currently looks as if the problems were localised, meaning specific locations across Europe and the US were affected.
Other websites knocked offline included: PayPal, Shopify, BBC.com, HBO Max, Vimeo