Beijing's top representative in Hong Kong said on Saturday that President Xi Jinping's speech had boosted people's confidence in the "one country, two systems" principle and countered smears against it.

The director of the Liaison Office, Luo Huining, made his remarks at a seminar a day after the president said the formula that has governed Hong Kong since the handover had proven to be successful and that there was no reason to change it.

Luo said the president had "set a definitive tone" on the matter by addressing questions on how long the blueprint will last.

He said Xi had boosted confidence among Hongkongers and members of the international community that it will continue to be implemented steadfastly and successfully.

"Those who worry that the 'one country, two systems' principle will change can now be reassured," Luo told an audience. "Those rumours that smear the principle has been self-defeated."

He added: "Looking into the future, no matter what the external interference or difficulties are, so long as we uphold the principle of 'one country, two systems,' to make sure it's not changed, shaken, bent and distorted, the principle will reach new heights."

Meanwhile, former chief executive CY Leung said Xi's speech showed that the year 2047 wouldn't be an expiry date for "one country, two systems."

He also said the two-day visit by Xi showed how much the state leader cares about Hong Kong.

"You can tell President Xi was not just reading from the script," Leung told Commercial Radio. "He showed his emotion when giving the speech. He cares a lot about this place."

The vice-chairman of the Chinese People's Political Consultative Conference added: "In the past two days, [Xi] didn't stay overnight. On his first day of visit, he stayed until quite late and returned to Shenzhen on an express train and came back the next morning. It's tough. The president not only oversees matters in Hong Kong, as you know, there has been major changes in the international situation."