The Secretary-General of the Federation of Students Nathan Law Kwun-chung, left, the founder of student activist group Scholarism Joshua Wong Chi-fung, centre, and Federation of Students activist Alex Chow Yong-kang stand outside the Eastern Law Courts Building in Hong Kong. Picture: EPA/ Jerome Favre

Hong Kong - Three pro-democracy activists went on trial in Hong Kong on Monday over charges relating to mass rallies in 2014, with the movement's student leader accusing the government of “unreasonable” prosecution.

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 as protesters called for free elections for Hong Kong's next leader.

Wong and two other prominent student leaders, Alex Chow and Nathan Law, appeared in court on charges of taking part in an unlawful assembly and inciting others to join it.

“It's unreasonable for the government to give us charges... we were just trying to protect our own rights,” he told reporters outside the court.

All three pleaded not guilty. They could face up to five years in prison if convicted.

“We are still confident to get a favourable outcome because we have persisted in peace and non-violence,” Wong told reporters.

“We believe finally we can find justice.”

Several police officers testified at Monday's hearing and the court saw video footage of protesters climbing over a gate to enter government headquarters.

Wong's lawyer Lawrence Lok said testimony by different police officers about the incident was almost identical.

“How do you explain the phenomenon? Is it a coincidence... was it copying?” Lok asked.

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.

Demonstrators called for fully free elections for the city's next leader.

But they failed to secure any concessions from the city government, which supported a Beijing-backed political reform package under which candidates would have been vetted by a loyalist committee.