Chief Executive John Lee on Saturday warned of existing national security risks even after the implementation of the security law, as he vowed to press ahead with legislation to enact Article 23 of the Basic Law.

At the opening ceremony of the National Security Education Day, Lee said activities endangering national security had gradually emerged and escalated since Hong Kong's return to the motherland.

But the implementation of the National Security Law, which Lee called a major turning point for the territory, had brought Hong Kong back to peace and stability.

He said the central government acted to end disruption, and peace had returned to the SAR, Lee said.

"There is still a small bunch of separatists who continue to plot against Hong Kong and work underground. Lately, there have been people arrested for publicly promoting violence, so we can see that there are still sub-currents that can pose a threat."

He said the government will further improve Hong Kong's system and enforcement mechanism in safeguarding national security, including enacting Article 23 of the Basic Law to introduce Hong Kong’s own national security legislation as soon as possible.

"We are also studying into crowd-funding, as well as other problematic actions. We would optimise the risk management for financial security," he said.

The director of the central government's liaison office in Hong Kong, Zheng Yanxiong, for his part, said it's vital for the city to have an in-depth review of the serious chaos in the past.

Zheng, who's also an adviser to the Committee for Safeguarding National Security, said the SAR can no longer afford to make any more major mistakes.

"Independence is a dead-end cause... Opposing the [Chinese Communist Party] will be a death sentence," he said. "We have to realise we have to consolidate the fundamentals for good governance."