BEIJING, July 6 (Reuters) - A Chinese city planned to censor online chatroom exchanges and ban anonymous postings after residents used the Internet to organise a mass protest against a chemical plant, Chinese media reported on Friday.

Under a new city regulation, online users would have to use their real names when posting messages on more than 100,000 Web sites registered in Xiamen, a port city in southeastern coastal Fujian province, the Beijing Youth Daily said.

"The names registered must be the same as the ones on your identity card," it quoted an unnamed government official as saying, adding postings would be screened in advance of being posted and any unacceptable material would be blocked.

Internet censorship is common in China, where the government employs an elaborate system of filters and tens of thousands of human monitors to survey its 140 million Internet users' surfing habits, surgically clipping sensitive content.

The government had been considering a regulation to require bloggers to use their real names when they register with Web logs, but backed down later following protests from the Internet industry and users.

Last month, thousands of protesters wearing gas masks and holding banners marched through Xiamen, demanding the government scrap plans to build a chemical plant some denounced as an "atomic bomb" threatening the seaside environment.

The citizens had organised the protest and exchanged information and comments through Web chatrooms, blogs and mobile text messages.

"After the protest against the project, the government thinks it should control the contents of the Internet," the official was quoted as saying.

"Those who illegally spread harmful or bad information will be detained or fined," the newspaper said, citing the planned regulation.

The Chinese government, obsessed with stability, has said Internet censorship is necessary to allow users to enjoy a "healthy" online environment and help build a "harmonious" society.

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