China has blocked a second internet search engine, less than a week after banning the hugely popular Google website.

Chinese internet users trying to use the AltaVista.com search engine have found it cannot be reached.

The site was inaccessible when tested by BBC News Online using a system developed by researchers at the Harvard Law School.

The measures comes ahead of a vital Communist Party meeting in November during which the country's leadership is expected to be overhauled.

Search ban

China maintains tight controls on the internet, muzzling the web as a forum for free information and discussion among its 45 million web users.

China has 45 million people online

It routinely blocks access to foreign news sites such as the BBC and frequently forces domestic sites to remove political material.

But this is the first time it has blocked search engines, which carry links to other sites but do not generally offer content themselves.

Google does keep its own archives of web pages, to make surfing faster and more efficient.

That search engine, which has a highly-popular Chinese language version, has been unavailable in China since the weekend.

Satellite action

Media freedom groups have expressed their concern, calling on China to lift the ban on Google.

Other search engines such as Yahoo.com are still available in China.

Yahoo is one of the 130 major web portals that recently signed a voluntary pledge not to post information that would jeopardise state security and disrupt social stability in China.

Beijing is also tightening up on satellite communications networks.

The authorities are planning nationwide checks on the unauthorised use of satellites networks and ground relay stations, said the state media on Thursday.