Chinese bloggers urged US Secretary of State John Kerry to push for greater freedom online in China during a rare meeting in Beijing Saturday, asking for help to "tear down the great Internet firewall".

The US embassy-organised discussion was an opportunity for the top diplomat to hear directly from China's bloggers amid reports that Beijing is stepping up efforts to clamp down on political dissent.

Chinese microblogs similar to Twitter have become key drivers of public opinion in recent years, with bloggers calling attention to issues such as official corruption and pollution that challenge the ruling Communist Party.

But the rising popularity of sites such as Sina Weibo has triggered a sweeping government-backed crackdown on online dissent in the past year, with several prominent commentators silenced and others arrested.

The meeting with four leading bloggers came a day after Kerry used talks with President Xi Jinping and Foreign Minister Wang Yi to call for Communist Party authorities to improve their human rights record.

In the roundtable Saturday, Kerry told bloggers that he had raised the issues of press and Internet freedom in his discussions with Chinese leaders.

"Obviously, we think that Chinese economy will be stronger with greater freedom of the Internet," he said.

- 'Tear down the firewall' -

In the 40-minute meeting, Zhang Jialong, who frequently comments on China's social conditions to his 110,000 microblog followers, urged the United States to support "Chinese who aspire for freedom" and help "tear down the great Internet firewall".

The finance reporter, who was detained for three days in 2011 for his postings on artist Ai Weiwei, also accused US companies of helping China block access to some Internet sites such as Twitter.

Kerry said he had no knowledge of such a practice but promised to investigate.

Wang Keqin, an investigative reporter who was fired from his job at the Economic Observer last year for his reports on flash floods that hit Beijing in 2012, told Kerry that Internet freedom "was going backward, there is less of it".

Kerry told reporters Friday that he had a "frank discussion" about human rights issues in his meeting with Chinese leaders, including the free flow of information online.

"I emphasised that respect for human rights and for the exchange of information in a free manner contributes to the strength of a society in a country," he said after the meetings in Beijing.

China's ruling party has long been engaged in a "cat and mouse" game with Internet users, tightening restrictions in periodic crackdowns before new forums emerge to challenge such restraints.

In August, Xi called on propaganda officials to "build a strong army... to seize the ground of new media", while China's press regulator has ordered journalists to undergo Marxist training classes, state media reported.

- Jail for online 'slander' -

China's Supreme Court in September said Internet users could face three years in jail if "slanderous" information spread online was viewed more than 5,000 times or forwarded more than 500 times.

The rising influence of microblogs has been accompanied by the emergence of celebrity users with verified accounts, known as "Big Vs".

Last year Chinese-American investor Charles Xue, who had more than 12 million followers on his microblog which was heavily critical of the government, was arrested on charges of soliciting prostitutes.

State media insisted at the time that his arrest had no connection with his online presence, but government-run broadcaster CCTV showed him in prison clothes while under detention, confessing that he had used microblogging to "gratify my vanity".

Microsoft's Bing search engine came under scrutiny this week following reports that Chinese-language searches for topics deemed politically sensitive by Beijing return a drastically different set of results than English-language searches -- both inside and outside of China.

Bing has denied censoring its Chinese-language search results outside China.

Kerry also visited a joint venture between Indiana-based Cummins and China's Foton company in Beijing producing low emissions diesel engines, before heading to Jakarta on the next leg of his Asia trip.