Media freedom groups have criticised China for blocking access to the popular search engine Google.

The New York-based Committee to Protect Journalists (CPJ) and the Paris-based Reporters Sans Fronti�res (RSF) both called on Beijing to lift the ban.

Chinese internet surfers have been unable to access the Google site since the weekend.

Google has said it is working with Chinese authorities in an attempt to remove the block.

'Very concerned'

The search engine is one of the most popular sites in the world and its Chinese language version was widely used in the country.

This move against Google strikes at the very ability to find information on the internet

Robert Menard, Reporters Sans Fronti�res

Beijing routinely blocks access to sites run by the banned spiritual movement Falun Gong, human rights groups and some foreign news organisations like the BBC.

But this is the first time it has banned a search engine, which carry links to other sites, but does not itself carry information.

It does however keeped a local copy of frequently visited webpages to make surfing faster and more efficient.

The CPJ said it was "very concerned", arguing the ban would adversely affect access to information for both journalists and other citizens in the country.

In an open letter, it called on China's President Jiang Zemin to reverse the block.

Blocking information

RSF has also pressed Beijing to allow access to Google.

"The authorities were already in the habit of using surveillance, censorship or the outright elimination of overly critical websites," said RSF Secretary-General Robert Menard in a letter to the Chinese authorities.

"But the blocking of a search engine sets a surprising and very worrying precedent.

"This move against Google strikes at the very ability to find information on the internet," said Mr Menard.

In online forums, Chinese internet users have spoken out against the ban on Google, saying they use it for research, not politics.

Beijing has made no direct comment on the ban, which comes just ahead of a vital Communist Party meeting during which the country's leadership could be overhauled.