Online encyclopaedia Wikipedia will shut down for 24 hours tomorrow to protest against US piracy laws, which are backed by the music and film industries but rigorously opposed by internet companies.

The Stop Online Piracy Act and Protect IP Act will force internet service providers to block non-US websites that offer pirated content if served with a court order.

Wikipedia founder Jimmy Wales announced the planned global block-out of the site's English pages on Twitter this morning, after first raising the idea on Monday.

"This is going to be wow. I hope Wikipedia will melt phone systems in Washington on Wednesday. Tell everyone you know!" he tweeted.