It came shortly after demonstrators kicked off a series of rallies billed as a global "emergency call for autonomy" in the semi-autonomous Chinese city, Efe news reported.
More than 1,000 activists, many wearing masks in defiance of a recently introduced law, fled from Victoria Park when riot police fired multiple rounds of teargas.
Officers accused the campaigners of violating the law by wearing masks and taking part in an "illegal assembly".
The police action forced a host of meetings in the park, which were legal and featured pro-democracy candidates running in an upcoming local election, to be cut short.
Several people were arrested, including two election candidates.
Undaunted protesters headed to Central, the main financial area of Hong Kong, to attend two other rallies.
The activists were responding to netizens' calls to join a range of pro-democracy activities in four different locations in the city, in tandem with dozens of cities across the world.
The protest on Saturday was meticulously and creatively planned to minimize the risk of participants being arrested by police, who have rounded up more than 2,600 people since the ongoing protest movement began nearly five months ago.
The election meeting in Victoria Park was an alternative form of anti-government rally planned by activists after they failed to secure police permission for a mass anti-government rally in the park.
By Hong Kong law, each election candidate meeting can accommodate no more than 50 people without requiring police approval.
As 128 candidates had signed up, the meetings could theoretically draw 6,400 people without breaking the law.
But riot police who arrived at the park in the afternoon insisted that participants were taking part in an illegal assembly.
After the teargas rounds, some election candidates spontaneously staged a protest condemning the police for targeting the lawful election meetings.
Scuffles ensued and riot police arrested two candidates.
Adrian Lau, one of the election candidates attending the meeting, told Efe: "This is beyond reason. We did nothing illegal by holding election meetings here today.
"We were peaceful throughout. But in a way, the police action was expected.
"Over the past months, they've violated rules and laws many times."
Tensions were already running high, with 100,000s protesters gathering in the main streets of Causeway Bay, where Victoria Park is located.
One of the rallies, held at Edinburgh Place, urged the United States to pass the Hong Kong Human Rights and Democracy Act, which would require Washington to annually assess Hong Kong's level of autonomy from Beijing and cancel its trading privileges if that autonomy is compromised.
Another demonstration, held in Chater Garden, was a peaceful origami-making event.
On the other side of the harbour, a group of pro-democracy activists gathered in the touristy area of Tsim Sha Tsui.
( With inputs from IANS )