Internet authorities in China have published a blacklist of more than 100,000 web addresses which have been used to send spam.

The online list is intended to help service providers and email recipients filter out spam.

China has been ranked as one of the world's most prolific sources of unsolicited commercial email by various sources, including online security firms.

The country has been criticised for being slow to react to the spam problem, and of ignoring reports of spam by local and international internet service providers.

The latest official action appears to have been prompted by complaints from inside China, particularly from users troubled by email-borne viruses.

Security firm Sophos reported a reduction in spam originating from or relayed through China earlier this year, suggesting that government anti-spam efforts were proving effective. 

The new blacklist has been built from IP addresses submitted by the public, according to Zhao Zhiguo, deputy director of the Chinese Ministry of Information Industry's telecoms department.

The list of offenders contains both local and international IP addresses, Zhiguo told the government-controlled Xinhua News Agency.

The ministry also plans to create a whitelist of recognised bona fide email senders, the reports said. Chinese anti-spam regulations of this nature have raised concerns that they could be used to suppress free speech.

China's new anti-spam website is not yet fully open to the public, according to Huang Chengqing, secretary general of the Internet Society of China, which manages the site. 

The Internet Society of China has reportedly sent an ultimatum to the operators of more than 900 local IP addresses, telling them to stop sending spam by 18 July or face unspecified consequences.