BEIJING, CHINA: Chinese mobile telephone users must register their personal details to buy phone numbers under a rule that comes into force from Wednesday, in what the government calls an attack on spam but some see as a blow to privacy.

The Ministry of Industry and Information Technology says residents buying numbers for mobile phones must now show their ID cards, and foreigners must produce their passports, with buyers limited to a maximum of 18 numbers.

Cell phone SIM cards are widely sold at shops and newspaper stalls in China for as little as 50 yuan ($7.30) each. The cheapest numbers heavy in the digit 4, pronounced 'si' in Mandarin Chinese, a similar sound to the word for death.

The China Daily newspaper said the move was "the latest campaign by the government to curb the global scourge of spam, pornographic messages and fraud on cellular phones".

Unsolicited text messages sent from mobile numbers offering cheap real estate, fake sales receipts, and miracle health products are a headache for many residents.

But the long-discussed move, similar to rules in some countries in the West, is opposed by critics who see it as another intrusion into privacy, making it easier for authorities to snoop. Others fear the information will be illicitly sold to spammers and other unscrupulous businesses.

"Now that the system of authenticating names for mobile phones is being enforced, the related measures for protecting citizens' privacy cannot be delayed," a commentary in the China Economic Times said.

China had 795 million mobile phone subscribers by the end of July, according to government estimates. They received an average 43 text messages every week, about 12 of them spam, the China Daily reported, citing a government centre tackling the problem.