Visitors to Wikipedia's English-language site were greeted by a dark page with white text which said: "Imagine a world without free knowledge... The US Congress is considering legislation that could fatally damage the free and open internet.

As of 5am on Wednesday, anyone trying to access the online encyclopedia will have been greeted with a blackened screen and a message exhorting them to "imagine a world without free knowledge".

In place of articles, (with the exception of those for SOPA and PIPA themselves) the site showed only a message in protest of SOPA and PIPA asking visitors to "Imagine a world without free knowledge."

Users attempting to access the site see a black screen and a political statement: "Imagine a world without free knowledge."