China's top official on Hong Kong affairs said the city should "tightly hold" onto the bottom line of national security to safeguard development, in a speech coming weeks after the enactment of sweeping new security laws.

"To move towards governance and prosperity, we need to tightly hold onto the bottom line of national security in order to safeguard the high quality development of Hong Kong," said the director of Beijing's Hong Kong and Macau Affairs Office, Xia Baolong, in a speech to mark an annual national security day.

Hong Kong in March enacted a new national security law, also known as article 23, that updates or introduces new laws to prohibit treason, sabotage, sedition, the theft of state secrets and espionage, with jail terms of up to life imprisonment.