The 73-year-old Lai, who is already in jail for other alleged offences, is accused of inciting others to participate in the unauthorised assembly in Victoria Park last year, Xinhua news agency reported. 

The 20 defendants appeared at the West Kowloon Magistrates' Courts on Friday. 

While two of the defendants prepared to confess, eight others pleaded not guilty and the rest 10, including Lai, were yet to decide. 

The court adjourned the case and will deal with their pleas, respectively. 

In addition to the defendants standing trial on Friday, there were six people also involved in the case, including pro-democracy activist Joshua Wong and three others, who have been sentenced to four to ten months in jail. 

The rest two, including activist Nathan Law, have fled Hong Kong. 

Arrest warrants have been issued for them.