China has blocked a second US-based Internet search engine, less than a week after the massively popular website run by Google was put out of action for mainland surfers, Internet users reported on Friday.

On Friday morning, Internet servers in Beijing and Shanghai were unable to access the Altavista.com search site, marking another apparent step in an information clampdown by Beijing ahead of a vital Communist Party meeting in November.

The 16th Communist Party Congress is expected to see a major changeover in the top echelons of China's ruling party, which could see President Jiang Zemin and other elderly leaders step down from power.

Beijing has declared a general security alert in the run-up to the meeting, while state-run media has noticeably stepped up its torrent of pro-Jiang propaganda.

Rights groups have condemned the block on Google, which began last weekend, with the New York-based Committee to Protect Journalists (CPJ) saying it was "very concerned" at the apparent Chinese action.

Google, which has a highly-popular Chinese language version, said Wednesday it was working with Chinese authorities in an attempt to remove the block.

"Our users have confirmed that we are being blocked in China. We are currently working with Chinese authorities to restore service," said spokeswoman Cindy McCaffrey.

The company had not received any specific information on why Google was being barred, she added.

A series of Chinese ministries and other official bodies which deal with the Internet and state security have consistently pleaded ignorance over the bar on the Google site, saying they knew nothing about it and were not responsible.

China routinely blocks a large number of foreign-based sites, primarily those featuring dissident views or banned groups such as the Falun Gong spiritual movement, but also certain foreign news sites and pages showing pornography.

However it has not previously blocked search engines, which carry links to other sites but do not generally carry information themselves, although Google possesses its own archives of Internet pages.

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