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...