Two pro-democracy activists took the stand in Hong Kong Thursday over charges relating to mass pro-democracy rallies in 2014, defending the movement as "peaceful".

Joshua Wong, 19, was the teenage face of the Occupy Movement, which brought parts of the semi-autonomous Chinese city to a standstill for more than two months when protesters called for free elections for the city's next leader.

The protests tapped into concerns about Beijing's growing influence in the former British colony, despite a guarantee that its civil liberties should be maintained for at least 50 years.

Hong Kong laws allow peaceful protests but the city's Public Order Ordinance criminalises gatherings of three or more who conduct themselves in a disorderly, intimidating, insulting or provocative manner, intended to cause fear.

Wong and two other prominent student leaders, Alex Chow and Nathan Law, have been charged with taking part in such an "unlawful assembly" and inciting others to join it. All three have pleaded not guilty.

The charges referred particularly to an incident leading up to the mass rallies when protesters climbed over fences to enter a restricted area in front of government headquarters.

"We gathered there to express our desire for democracy... I have always followed the principles of peacefulness, rationality and non-violence," Wong told the magistrates court where the spectacled university student was tried for the September 26, 2014 protest.

"Every person in Hong Kong should have the right to organise protests, marches or public assembly," he said.

A total of 955 people were arrested throughout the Occupy movement, according to authorities. Hundreds were injured in clashes between police and protesters.

Wong was charged nearly one year after the event.

Law, another student leader, said residents' calls for free elections were "ignored".

"We needed to take action," he said.

David Leung, the government prosecutor, said protesters threatened public order.

"Violence was definitely involved," he said.

The three could theoretically face up to five years in prison if convicted, although the magistrates court where they were tried would only impose a jail term of three years at maximum.

Wong is facing several other charges, including obstructing police, over his participation in the pro-democracy rallies.

He has also been charged with contempt of court for violating an order to clear the Mongkok protest camp -- scene of some of the most violent clashes during the demonstrations.

Wong has said he is the target of "political prosecution" and a "witch hunt" against those at the forefront of the Occupy Movement.

The months-long protests failed to secure any concessions from the city's government, which supported a Beijing-backed political reform package under which candidates would have been vetted by a loyalist committee.

Hong Kong was returned from Britain to China in 1997 under the "one country, two systems" arrangement, guaranteeing the city's freedoms unseen on the mainland.