Amnesty International condemned Tuesday the forthcoming trials of eight anti-corruption activists in China, calling them "hypocritical" and saying they highlighted flaws in the ruling Communist Party's much-publicised anti-graft campaign.

Starting Wednesday with the case of Xu Zhiyong, one of China's most prominent current dissidents, the eight New Citizens Movement members face possible five-year prison sentences in separate trials this week.

They are being prosecuted over peaceful protests in which they held up banners calling for government officials in China to disclose their financial assets, seen by some as a reform which would combat corruption.

Since taking over as head of the Communist party in November 2012 Xi Jinping has repeatedly vowed to combat endemic graft in the country's political system, with state-run media covering the campaign extensively.

But Chinese authorities do not tolerate any organised activity that might develop into a challenge to their rule, and campaigners say the trials are intended as a warning to others.

"Instead of President Xi Jinping's promised clampdown on corruption, we are seeing a crackdown against those that want to expose it," Roseann Rife, East Asia research director for London-based Amnesty International said in a statement headed "China: Hypocritical crackdown on anti-corruption campaigners".

The activists on trial this week, including lawyers and several businessmen, are part of a loose-knit group referred to as the New Citizens Movement which was founded by Xu, a well-known lawyer and human rights campaigner.

"We consider Xu Zhiyong to be a prisoner of conscience and he should be released immediately and unconditionally," Rife said.

"Anything less would make a mockery of the Chinese government's ongoing anti-corruption efforts," said Rife. The activists were on trial "simply for exercising their rights to assembly and free speech", she added.

The US and the EU's outgoing China envoy have both condemned the arrest of Xu, a trained lawyer and lecturer at a university in Beijing.

But China's foreign ministry spokesman Hong Lei dismissed US criticism as "interference in China's internal affairs".

Xu called for a New Citizens Movement in an 2012 article, and urged Chinese to spread a "New Citizen spirit" by filing lawsuits, photographing injustices and in some cases carrying out street protests.

Members also held dinners in an estimated 30 cities with 20 to 200 people attending each, activists say.

Rights groups estimate that between 20 and 40 people connected with the movement have been detained since last year, including billionaire businessman Wang Gongquan, a friend of Xu who was held in September.

At least three have already been put on trial. Xu and the others are accused of "assembling a crowd to disrupt order in a public place" for their role in the street protests.

Governments and rights groups have reported a tightening of restrictions on dissent and the media since Xi assumed the party's top post.