BEIJING (AFP) - Strict security was imposed outside a courthouse in Beijing on Wednesday ahead of the trial of Xu Zhiyong, one of China's most prominent dissidents, for his part in anti-corruption protests.

Xu, founder of the New Citizens Movement, faces a five-year jail term on charges of "assembling a crowd to disrupt order in a public place" for protests which saw activists display banners calling for asset disclosure by officials - seen as a key measure against graft.

Dozens of police, in uniform and plain clothes, surrounded the court in western Beijing, harassing reporters and trying to prevent them filming in front of the court building.

Xu is one of eight New Citizens Movement activists due to stand trial this week in what has been viewed as part of a government crackdown on dissent.

They are all almost certain to be found guilty by China's politically controlled courts.

The trials come despite a much-publicised anti-corruption drive by China's Communist party under Xi Jinping, and overseas rights groups have condemned the proceedings as "hypocritical".

At least 20 of Xu's supporters from across China gathered near the court, with a group of around 10 unveiling a red banner calling for officials to disclose their assets - similar to the actions which have led to Xu's trial.

"If you don't expose your assets, it shows you must have a secret," said one of them, Wu Guangzhong. "Declaring assets is the most common way of preventing corruption."

Zhu Jiaqi, 64, from Tianjin, added: "It should be an open trial but it's held in secret. Xu's voice reflects the voice of the basic and ordinary people."

Foreign diplomats were allowed into the court building, but were told they would not be permitted to attend the hearing itself, one European representative told AFP.

Between 20 and 40 people involved with the New Citizens Movement have been detained since last year, according to members, while at least three have already been put on trial.

The arrests have been seen as part of a wider campaign to enforce ideological unity since Xi became the head of the Communist party in late 2012.

"The Chinese Communist Party reinforced its monopoly on power in 2013 through tough new measures and hardline rhetoric, dashing hopes that the country's new leadership would engage in deep systemic reforms to improve human rights and strengthen the rule of law," Human Rights Watch said in a statement this week.