Thousands of students braved sweltering heat Monday to demand greater democracy in Hong Kong as they launched a weeklong boycott of classes, underscoring a restive younger generation's determination to challenge the Chinese Communist Party.

Dressed in white and wearing yellow ribbons, students from more than 20 universities and colleges packed into the grounds of picturesque, bay-side Chinese University where they were greeted by banners that said: "The boycott must happen. Disobey and grasp your destiny."

Managing the former British colony 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.