Hong Kong pro-democracy protest leader Joshua Wong and two other members of his student group Scholarism announced Monday they have gone on an "indefinite" hunger strike, starting immediately.

"Living in these troubled times, there is a duty. Today we are willing to pay the price, we are willing to take the responsibility," the students wrote in a declaration on Facebook, after announcing the hunger strike on stage at the main protest camp outside government headquarters in central Hong Kong.

Along with 18-year-old Wong, female Scholarism members Lo Yin-wai, a university student and Wong Tsz-yuet, 17, a secondary school pupil, said they are fasting to attempt to force the Hong Kong government to respond to their demands for free elections in the semi-autonomous Chinese city in 2017.

"Our future, we will take it back," they wrote.

The trio are calling on Hong Kong authorities to reopen stalled talks with students and for the Chinese government to withdraw its decision to vet candidates for leadership of the city.

"We, Scholarism, announce that now I, Joshua Wong, Wong Tsz-yuet and Lo Yin-wai, the three representatives, will go on an indefinite hunger strike," Wong told protesters from the stage at the main protest camp in the Admiralty district.

The bespectacled 18-year-old firebrand has become one of the most prominent faces of the two-month-old 'Umbrella Movement' and is in the running to be named TIME Magazine's Person of the Year.

The three youngsters will drink only water during the strike, a local television station reported.

The announcement comes as protesters struggle to find new ways to push forward their demands for full democracy, as Hong Kong authorities order the clearance of key protest zones.

The previous 24 hours saw some of the worst violence to hit the protests in weeks, with police using pepper spray and batons on students trying to storm government headquarters.

With the student-led protests now into their third month and frustrations mounting, Hong Kong Chief Executive Leung Chun-ying hinted that further police action may be imminent, in his most forceful comments in recent weeks.

"I have pointed out before that Occupy Central is not only illegal but it will also be in vain," Leung told reporters Monday, describing the continued protests as "intolerable".

On Monday afternoon the Hong Kong high court granted an injunction ordering the clearance of several parts of the main protest camp in Admiralty, according to bus operator Kwoon Chung, which made the application.