SINGAPORE - It is the responsibility of Hong Kong and Beijing to make one country, two systems work, and if other parties get involved, it will not be helpful, said Prime Minister Lee Hsien Loong on Friday night.

This was his response, at the National University of Singapore Society (NUSS) Lecture, when asked by an audience member about the demonstrations in Hong Kong.

Mr Lee noted that the one country, two systems approach has "created areas for interpretation" since it is not easy to draw clear boundaries.

"Where exactly does one country end and two systems begin? So Hong Kong people as well as the central government in Beiing have to (make it work) jointly. It's a delicate situation," he said.

But he warned that if other parties were involved and used the occasion to "pressure or change" China, the situation could get complicated.

Giving an example, Mr Lee said he had read news reports that former activists who were involved in Beijing's Tiananmen protests in 1989 had gone to Hong Kong to give advice to student protestors there.

"I don't think such help is helpful in any way," he said.

Mr Lee noted that the "geo-political reality is that Hong Kong is now part of China", and that China is prepared to "go very far" to help Hong Kong succeed.

But it would not want Hong Kong to "become a problem on the other side of the Shenzhen river".

Tens of thousands of people have taken to the streets of Hong Kong, since Sunday night, to push for universal suffrage. They are against election restrictions that will see Bejing vet candidates for elections in Hong Kong.