Thousands of Hong Kong students boycotted classes on Monday to protest against Beijing’s decision to restrict electoral reforms in a week-long strike marking the latest phase in the battle for democracy.

Students from more than 20 universities and colleges streamed into the grounds of the Chinese University of Hong Kong, where they were greeted by banners saying: “The boycott must happen. Disobey and grasp your destiny.”

Many of the students were dressed in white and wearing yellow ribbons. Some sat in a circle playing guitars in temperatures close to 86F (30C), while others prepared leaflets urging students to boycott classes.

Students attend a rally at the Chinese University of Hong Kong campus. Photograph: Vincent Yu/AP

“On 31 August, when the National People’s Congress made their decision, it crushed the dreams of some Hong Kong people who have been fighting hard for democracy for the past 30 years,” said third-year student Hong Yuen.

After months of rallies and protests, a survey by the Chinese University found that more than a fifth of Hong Kong residents are considering leaving the city, spurred by concerns about its political future.

Just over 21% of the 1,006 respondents said they would consider emigrating. The last major emigration from Hong Kong was just before it was returned to Chinese rule in 1997.

Students carry a banner during the rally at the Chinese University on 22 September in Hong Kong. Photograph: Lam Yik Fei/Getty Images

A former British colony, Hong Kong was given wide-ranging autonomy and an undated promise of “universal suffrage” when it was returned to China under a “one country, two systems” form of government.

Now, activists are demanding a fully democratic election for the city’s next chief executive in 2017, while Beijing says it will only allow residents to pick between pre-screened candidates selected by a pro-Beijing nominating committee.

Managing Hong Kong is proving a challenge for Beijing, which is worried that calls for democracy in Hong Kong and the nearby former Portuguese colony of Macau could spread to cities on the mainland, threatening the Communist party’s grip on power.

On average, survey respondents said they did not trust the Hong Kong or Beijing governments. Young people with higher levels of education felt most strongly.

However, fewer than a third of respondents said they supported the Occupy Central with Love and Peace movement, which plans to shut down the city’s central business district to press its demand for fully democratic elections in coming weeks.

The survey, based on telephone interviews with Cantonese-speaking Hong Kong residents, was organised by the university’s Centre for Communication and Public Opinion, and conducted between 10 and 17 September.

Thousand of students gather to mark the start of the boycott. Photograph: Lam Yik Fei/Getty Images

Leading academics in Hong Kong have voiced support for the boycott, with some offering to record lectures and post them online for students who miss classes.

The boycott is being organised by groups including the Hong Kong Federation of Students and Scholarism.

The boycott coincides with a trip to Beijing by some of Hong Kong’s most powerful business tycoons, where they are expected to discuss the area’s politics with Chinese leader Xi Jinping.