A Chinese newspaper at the centre of rare protests over government censorship last January when its New Year message was altered insisted on its right to "express the truth" in this year's article Thursday.

The row at the Southern Weekly newspaper blew up when an article urging greater protection of people's rights was replaced by one praising the ruling Communist Party.

Demonstrators massed outside the offices of the popular liberal newspaper in the southern city of Guangzhou, in a rare stand-off against authorities over media freedom.

This year's New Year message focused on the newspaper's values in fighting for truth on its 30-year anniversary.

It took a largely philosophical tone, and did not contain any overt mention of last year's incident or any reference to the government's propaganda machine.

But it said: "As a newspaper that strives for the truth, we are sometimes powerful as well as powerless.

"But we have no choice... but to question, and express the truth industrially, professionally and responsibly," it added.

China was going through a period of "great rejuvenation" and "transformation", it said, but warned that presented an opportunity for "what is false to pretend to be real".

Nonetheless some readers were underwhelmed by what the newspaper described as its 'New Year Congratulatory Message'.

"Compared with previous years' messages, this is really pathetic," said one poster in a comment under the article.

Others said it was "a little disappointing" and "lacks power".

Some reader comments did back the newspaper, with many simply saying: "Carry on -- we support you!"

Public challenges to the authorities on issues of press freedom are rare in China and the affair was seen as one of the first tests for the new party leadership under Xi Jinping, which has since launched crackdowns on dissent.

At the peak of the protest, demonstrators numbered in the hundreds and the campaign won support online, including from celebrities with millions of followers on China's Twitter-like weibo social networks.

All Chinese media organisations receive instructions from government propaganda departments, which act to suppress news seen as "negative" by the ruling party. But the censorship of Southern Weekly was seen as unusually direct.

China came 173rd in a press freedom ranking of 179 countries issued by the advocacy group Reporters Without Borders last year, climbing one place on the previous year.