Hundreds of people demonstrated in support of media freedom in China on Monday outside the offices of a newspaper at the centre of a censorship row, in a rare public display of anger on the issue.

The protesters were outside the Southern Weekly's office in Guangzhou, with one banner reading: "We want press freedom, constitutionalism and democracy".

The demonstration in the southern city came after censors on Thursday blocked a New Year article in the popular liberal newspaper which called for the realisation of a "dream of constitutionalism in China" to protect rights.

Some of the journalists working at the newspaper said they intended to strike over the row in Internet postings on Sunday evening.

All Chinese media organisations are subject to instructions from government propaganda departments, which often suppress news seen as "negative" by the ruling Communist Party, although some publications take a more critical stance.

On Friday a liberal Chinese journal's website, Annals of the Yellow Emperor, was shut down after it published an appeal for leaders to guarantee constitutional rights, including freedom of speech and assembly.

The crackdown on freedom of expression comes despite pledges of change from the new leadership, headed by president-in-waiting Xi Jinping, which has promised a more open style of governance since the Communist Party congress in November.

Police allowed the demonstration, which was made up of mainly young people who were carrying posters and scattering chrysanthemums, a flower used at funerals in China which has become the protesters' symbol for the loss of press freedom.

The censorship at the Southern Weekly sparked online uproar from netizens, including the newspaper's staff.

Some Internet reports said strike action was agreed by staff after senior editors took control of the newspaper's posts on Weibo, China's version of Twitter, from day-to-day journalists.

In Washington, in response to a question on the demonstration, State Department spokeswoman Victoria Nuland urged greater media freedom for Chinese journalists and international correspondents working in China.

"We believe that censorship of the media is incompatible with China's aspirations to build a modern information-based economy and society," Nuland said.

"It is, of course, interesting that we now have Chinese who are strongly taking up their right for free speech, and we hope the government is taking notice."

Searches for Southern Weekly on the popular microblogging site were blocked on Monday.

A Chinese-language editorial in the state-run Global Times, which has links to the ruling party, said Beijing was determined to maintain the status quo when it came to the media.

"No matter whether these people (angered over the censorship) are happy or not, a common sense is that it is impossible to have the kind of 'free media' they dream of under China's social and political reality today," it said.

"The media will by no means become a 'political special area' in China."

The media would "undoubtedly be a loser" if it sought to fight the government, it said.

The commentary did not run in the paper's English-language edition.

It followed an open letter from staff at the Southern Weekly which -- in an unusually vocal and public response to the authorities' moves -- called for the resignation of provincial propaganda official Tuo Zhen, who was said to have removed the New Year message and replaced it with a weaker article.

Another letter, signed by scores of prominent academics from across China, emerged over the weekend. This also called for the immediate removal of Tuo and for more press freedom.

An account of the strike by the Hong Kong-based China Media Project said journalists had also objected to a message by senior editors that the replacement New Year editorial had been "written by editors at the paper".

Asked about the Southern Weekly article at a regular press briefing last week, a foreign ministry spokeswoman in Beijing said: "There is no so-called news censorship in China."

China came 174th in a list of 179 countries ranked for press freedom in 2011-12 by the advocacy group Reporters Without Borders.

Also on Monday, a German correspondent investigating a recent case of five children killed by carbon monoxide poisoning in southwest China reported his computer and smart phone had been sabotaged after his hotel room was broken into.