A Hong Kong court denied bail on Monday to the first person charged with inciting separatism and terrorism under the city's new national security law after he carried a sign saying "Liberate Hong Kong" and drove his motorbike into police.

Tong Ying-kit, 23, was arrested after a video posted online showed him knocking over several officers at a demonstration last Wednesday, less than 24 hours after Beijing imposed sweeping national security legislation on its freest city.

The city's government has said the protest slogan "Liberate Hong Kong, revolution of our times", connotes separatism or subversion under the new law, stoking concern over freedom of expression in the former British colony.

Tong, who was unable to appear in court on Friday as he was being treated in hospital for injuries sustained in the incident, appeared in court in a wheelchair.

In rejecting bail, Chief Magistrate So Wai-tak referred to Article 42 of the new law, which states that bail will not be granted if the judge has sufficient grounds to believe the defendant will continue to endanger national security.

The case was adjourned until Oct. 6 and Tong was remanded in custody.

Critics say the law - which punishes crimes of secession, subversion, terrorism and collusion with foreign forces with up to life in prison - is aimed at crushing dissent and a long-running campaign for greater democracy.

Authorities in Beijing and Hong Kong have repeatedly said it is aimed at a few "troublemakers" and will not affect the rights and freedoms that underpin the city's role as a financial hub.

Also on Monday, prominent democracy activist Joshua Wong pleaded not guilty to inciting others to participate in an unlawful assembly during anti-government protests last year.

Fellow activist Agnes Chow pleaded guilty to a similar charge. Their case has been adjourned to Aug. 5.

Wong and Chow, who were both granted bail last year, led a pro-democracy group called Demosisto that they dissolved hours after Beijing passed the national security law.

The United States, Britain and others have denounced the new legislation, which critics say is the biggest step China has taken to tighten its grip over the city, despite a "one country, two systems" formula meant to preserve its freedoms.