Wong, 18, and two young female members of his Scholarism student group announced the "indefinite" hunger strike hours after Hong Kong's leader warned that the two-month-old protests are "in vain".
Student-led demonstrators are demanding free leadership elections for the semi-autonomous Chinese city, with the main protest camp continuing to block a long stretch of a multi-lane highway in central Hong Kong.
China's communist authorities insist that candidates for the 2017 vote must be vetted by a loyalist committee, which the protesters say will ensure the election of a pro-Beijing stooge.
Civil servants were forced to stay at home this morning and the city's legislature was suspended after protesters broke through police lines and occupied a major road outside the complex overnight.
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Wong, one of the most prominent faces of the so-called "umbrella movement", said he was launching a hunger strike alongside university student Isabella Lo, 18, and 17-year-old high school pupil Prince Wong in a bid to force the government to respond to their demands.
"Our future, we will take it back."
Wong, who is in the running to be named TIME magazine's person of the year, called on Hong Kong authorities to reopen stalled talks with students and for Beijing to withdraw its decision to vet candidates for the vote.
But the announcement came just hours after Hong Kong's leader Leung Chun-ying warned that the "intolerable" protests will come to nothing and hinted that further police action may be imminent, in his most forceful comments of recent weeks.
On Monday the high court granted an injunction ordering the clearance of several parts of the main protest camp in the Admiralty district, according to bus operator Kwoon Chung, which made the application.
A smaller camp continues to block another busy road in the shopping district of Causeway Bay.
Police cleared a third site in working-class Mongkok last week, making more than 140 arrests, but sporadic scuffles have continued there between police and crowds of angry demonstrators.