It was the first use of tear gas in more than a week after a series of mostly peaceful demonstrations in the semi-autonomous region.
The development came a day after 29 people were arrested after overnight clashes that saw authorities using tear gas to disperse the crowd.
Some protesters yesterday were seen throwing bricks and petrol bombs at riot police, who responded with tear gas. Other protesters set up roadblocks with bamboo scaffolding and tore up "smart" lamp posts equipped with surveillance cameras.
Police said in a statement on Sunday they strongly condemned protesters "breaching public peace" and that 19 men and 10 women were arrested.
More than 700 people have been arrested since the demonstrations began over two months ago after the pro-Beijing administration of Hong Kong announced a controversial extradition bill that would have allowed authorities to send criminal suspects to mainland China for prosecution, according to Al-Jazeera.
That bill has since been shelved, but protesters have continued their calls for more democracy in the special administrative region, demonstrating against the increased influence of China's mainland on daily life in the Asian financial hub.
They say they are fighting the erosion of the "one country, two systems" arrangement that enshrines a high degree of autonomy for Hong Kong since the handover to China.