Internet traffic and websites worldwide have been hit by the effects of superstorm Sandy which has damaged data centres or cut their power, industry sources said Tuesday.

On Monday evening the storm slammed into the East Coast of the United States, causing power cuts and heavy flooding in a zone where some 150 data centres are situated, in the states of Virginia, New Jersey and New York, according to a tally by the site Datacentermap.

Data centres, which house and treat computer data, are the nerve centres housing the servers that contain companies' strategic data and through which there flow the data from telecommunications operators and online content sites.

"Thousands, even tens of thousands of Internet sites, of all sizes and worldwide are unavailable," a senior employee of a European operator who did not want to be identified told AFP.

For example, the French Huffington Post site posts a message that, due to power outages caused by superstorm Sandy, its own website is experiencing technical difficulties.

Popular sites such as the American site (news and personalities), the chat platform Zopim and the specialist site CafeMom, could not be accessed.

Several of the sites that are inoperative are housed by the US company Datagram, based in New York and hit by the storm.

A graphic sent to AFP by an operator analysing on an hourly basis the activity of one East Coast Internet hub showed that traffic had peaked strongly on Monday evening as users logged on seeking news. It fell back some hours later as a result of power cuts and network failures caused by the storm.

Most data centres switched to back-up fuel-driven generators but these can rapidly run dry because the largest centres consume colossal amounts of power, the equivalent of that used by a medium-sized town.

The Franco-American company Cedexis is a kind of Internet switching operator which redirects requests and data flows of content publishers to the best centres according to the traffic.

It said its customers were "automatically redirected to data centres or content providers located outside the Sandy zone, as is always the case when we detect an anomaly."