A leading Chinese rights activist who organised rallies for media freedom pleaded not guilty to charges of disturbing public order in an all-night trial in which the judge rejected his requests for food, a lawyer said.

The case against Yang Maodong, 48, comes amid a broadening crackdown on dissent. In January, a Beijing court sentenced legal activist Xu Zhiyong to four years in prison for leading a loosely organized civil movement. Several of his followers also were imprisoned.

New York-based Human Rights Watch called on authorities to drop the charges against Yang, better known by his penname Guo Feixiong, and fellow defendant Sun Desheng, who was arrested for urging the Chinese government to grant more rights to its people and to disclose officials’ assets.

Zhang Lei, lawyer for Yang, said on his microblog that the trials on Friday against Yang and Sun at Tianhe district court in Guangzhou got off to a tense start when the court several times cut off arguments by the defence. The hearing ended only at 2:50am on Saturday with the judge granting a recess after Yang nearly fainted from hunger. The court had repeatedly rejected earlier requests for food, Sun’s lawyer Chen Jinxue said.

The lawyers said both Yang and Sun had been mistreated in detention. Yang was denied any outdoor break for 469 days, and Sun had his ankles and wrists shackled for a week before the trial, Zhang said.

A court employee declined to confirm the trials, but he said a “special case” was taking place, without further elaboration. Rights lawyers and advocates said security was heavy around the courthouse and stretched as far as 3km (1.9 miles) out.

Yang has advocated for greater political freedom and more civic engagement in China. In January 2013, he helped organise demonstrations and spoke in support of the editorial staff at the newspaper Southern Weekly in Guangzhou after its journalists said a new year’s message that called for rule by the constitution was altered because of censorship.

The charge alleges he gathered crowds to disrupt public order, but his supporters say the rallies were orderly.

He also encouraged activists to hold up placards in several cities. To avoid confrontation with police, the activists typically did not linger but left quickly after taking photographs of their acts, then posting the images online. Authorities have found such acts unacceptable, and Chinese courts have actively prosecuted the quick protests.

Sun was not involved with the Southern Weekly rallies, but his charge – the same as Yang’s – stems from his unfurling banners calling for public disclosure of officials’ assets and urging China’s legislature to ratify the International Covenant on Civil and Political Rights, Sun’s lawyer Chen Jinxue said.