Chief Executive Leung Chun-ying says Beijing will not accede to demonstrators' demands for democratic reforms. Meanwhile, activists have vowed a new phase of civil disobedience on Wednesday.
Pro-democracy protesters are downloading a fast-growing app called FireChat to stay in touch. It has been used around the world during political unrest.
Thousands of protesters used umbrellas to deflect tear gas canisters as authorities tried unsuccessfully to break up demonstrations in the city's Central business district.
Video footage from earlier in the day showed protesters using umbrellas to try to deflect pepper spray and water cannons as officers attempted to disperse the crowd.
The activists plan to stay out of university classrooms this week to protest Beijing's plan to screen candidates for the territory's next chief executive.