In a demonstration of the depth of disquiet at the Chinese government's repressive policies, 74 Chinese scholars have signed a public letter calling for widespread reforms.

Warning of "violent revolution" if their demands are not urgently heeded, the academics pointed out that political reforms have lagged behind the nation's economic expansion.

"If reforms to the system urgently needed by Chinese society keep being frustrated and stagnate," they wrote, "then official corruption and dissatisfaction in society will boil up to a crisis point and China will once again miss the opportunity for peaceful reform, and slip into the turbulence and chaos of violent revolution."

Reports of the letter being circulated on the internet within China came as one of the nation's most fearless dissidents and two of his colleagues succeeded in breaking the blockade around the home of Liu Xia, wife of Liu Xiaobo, the Nobel Peace Prize winner who is serving an 11-year sentence for subversion. Ms Liu has been kept in unofficial detention in her home for the past two years, but a YouTube video captures the moment when the dissident Hu Jia, who has himself served jail time for subversion, barges past guards to gain access to Ms Liu's apartment building.

The signatories of the public letter include lawyers and well-known legal experts at leading Chinese universities. They wrote that democracy, the rule of law and respect for human rights are "a global trend that could not be stopped".

Their letter went on: "China's 100 years of bloody and violent history – especially the painful and tragic lesson of the decade-long Cultural Revolution – show that once we go against the tide of democracy, human rights, rule of law and constitutional government, the people will suffer disaster and social and political stability will be impossible."

The circulation of the letter comes two months after Xi Jinping replaced Hu Jintao at the apex of the Chinese Communist Party, in a carefully-planned changing of the guard. In a recent speech, Mr Xi drew attention to the need for human and constitutional rights to be guaranteed.

He said: "All citizens are equal before the law … to fully implement the Constitution is the primary task and the basic work in building a socialist nation ruled by law."

He also recently chaired a meeting of the powerful Politbureau, which has committed to curbing "extravagance by officials and reduce bureaucratic visits and meetings". Analysts say it is too early to know whether these are mere words or whether, in this moment of political flux, real change may actually be afoot.

"We have come to that period again when the leadership is changing," He Weifang, professor of law at Beijing University and one of the letter's signatories, told Reuters news agency. "People expect continuing advances when it comes to reform of the political system. The Chinese people, including intellectuals, have been talking about this for a while, but little has happened. So I think we have the opportunity now to push it again."

However, in a sign of business as usual, references to the letter were removed from Chinese media reports.

Earlier this month, 12 Chinese were among 41 writers given awards by Human Rights Watch for their efforts to promote free expression despite official persecution.

Rights and wrongs: China's big issues

Freedom of speech

Although provisions to protect free speech exist in law, state censorship is a part of everyday life, as is the persecution of dissidents.

Land reform

Local governments in China can seize land from owners, and often pay little or no compensation for it. The issue has been a major and long-running source of social unrest, and state media reports that Beijing intends to pass legislation this year to prevent such land-grabs.

Economic reform

President Hu Jintao promised in his new year address to "improve the quality and efficiency of the economy". It is the area most likely to see change, after seven quarters of slowing growth.