Hong Kong may see national security threats arising from foreign interference aimed at undermining China's development in the face of geopolitical tensions, a legal expert has warned.

Lawyer Thomas So, a former president of the Law Society, also said safeguarding national security is not a "one-off job" while urging the government to continue explaining the city's security legislation to people at home and abroad.

In 2020, China's top legislature passed a bill to enact the national security law in Hong Kong to criminalise acts of secession, subversion, terrorism and collusion with foreign forces.

Five years on, So cautioned that the SAR's free and open economy made it "more vulnerable" to certain national security risks.

"It's easier for [foreign] interference to go through Hong Kong, if there is any plan from any foreign forces to try to suppress China's development and to endanger China's overall national security," he told RTHK.

"When we are dealing with different forms of foreign interference, they might not come in the same way as one saw back in 2019. We need to be highly alert because of the special situation Hong Kong is in."

He also said the administration should double down on its efforts to explain the city's national security legislation.

"We need to continue to do that, explaining this continuously not only to Hong Kong people, but also to people abroad, particularly business people, foreign government officials," he said.