A number of major websites around the world have been suffering outages - including the UK government site, The Irish Times, Amazon and many news websites.
It's thought to be caused by a fault at cloud computing firm Fastly, which says it's fixing an issue.
Some of the sites have already come back online.
Technology Correspondent Jess Kelly says work is ongoing to establish the cause of the outage.
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"At this moment in time it's not quite clear.
"It looks like it could be the host provider - Fastly is a company that hosts website like New York Times and so on.
"At this time we do not know, but we do know a significant portion of websites are not available."
