The central leadership has its constitutional rights and responsibilities regarding the political structure of Hong Kong, the city's chief secretary told a group of students on Tuesday who have initiated illegal protests that have blocked streets for three weeks.

Voters in Hong Kong could select their leader, for the first time by universal suffrage in 2017, according to a resolution adopted by the National People's Congress Standing Committee on Aug 31.

The "ultimate aim" of universal suffrage is enshrined in the Basic Law, in which nominees for the city's next leader will be produced by a "broadly representative nominating committee in accordance with democratic procedures". Rules were set out for this committee in the resolution adopted in August.

But protesters, who have camped out unlawfully on Hong Kong's main streets since Sept 28, want this decision withdrawn to allow electors to nominate candidates for the 2017 election. This method has been officially ruled as unconstitutional.

Chief Secretary Carrie Lam Cheng Yuet-ngor, speaking to core members of the Hong Kong Federation of Students in two-hour talks with government officials, maintained that the arrangements for the 2017 election must adhere to the constitutional framework.

Lam appeared puzzled as a student leader alleged that the top legislature's decision is "undemocratic". She said that having the city's leader popularly elected is a "historic leap".

She reiterated that Hong Kong is not an independent entity — it is a special administrative region of the country underpinned by the "one country, two systems" principle.

"The central leadership has its constitutional rights and responsibilities regarding the political structure of Hong Kong," she said.

In a four-point response to students, the administration said there is still ample room to refine details for the 2017 election arrangements to make the poll competitive and transparent. This is also not the "ultimate" blueprint for elections in 2022 and beyond.

The government also plans to submit a report to the State Council's Hong Kong and Macao Affairs Office to sum up recent events in Hong Kong in which it mulls a cross-partisan platform to build consensus for the democratic process in the long run.