Demosisto members Nathan Law and Agnes Chow also said they were stepping down from the group.
China says the national security should worry only those who don't abide by the legislation but Hong Kong democracy activist Joshua Wong says he will be targeted.
The Polytechnic University stand-off is one of the more dramatic episodes in six months of unrest that began in June with protests over an extradition bill seen by many in Hong Kong as an erosion of freedoms.
Wong became the poster child of the huge pro-democracy "Umbrella Movement" protests of 2014. Wong and his party, Demosisto, have denied supporting independence for the city.
Malaysian PM Mahathir Mohamad called for Carrie Lam to quit after she invoked colonial-era emergency powers to ban protesters from wearing face masks. Her move to quell months of unrest sparked immediate rallies and vows to defy the new law.
A massive pro-democracy rally in downtown Hong Kong ended early after violence broke out, with police firing tear gas and a water cannon after protesters threw bricks and Molotov cocktails at government buildings.
Yale-NUS College cancelled the "Dialogue and Dissent in Singapore" programme two weeks before it was scheduled to start.
Meeting between Germany's foreign minister and Hong Kong activist Joshua Wong will damage Germany's ties with China, Beijing's envoy to Berlin says, in an unusually direct verbal attack on an important trade partner.
Rows of students and alumni joined hands chanting "Hong Kong people, add oil", a phrase which has become a rallying cry of encouragement for the anti-Beijing protest movement.
Hong Kong leader Carrie Lam says she never tendered her resignation to China over the anti-government protests because that would be the "easy way out".
Police fired tear gas from the other side of the barriers, then brought out a water cannon truck that fired regular water and then a blue liquid at protesters.
Au Nok-hin and Jeremy Tam were arrested on suspicion of obstructing police, Tam's Civic Party said on its verified Facebook page.
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