Three Hong Kong pro-democracy lawmakers were arrested and then released Monday over their involvement in mass protests for free elections, the latest targets of a police probe campaigners say is tantamount to intimidation.

Police have vowed to investigate the "principal instigators" of the street blockades that ended in December when rally camps were cleared.

Hong Kong police arrested 33 people and fired pepper spray during clashes with demonstrators that disrupted traffic Sunday, as a protest at the rising number of visitors from mainland China turned violent.

Local residents are becoming increasingly angry at border-crossing Chinese traders, whom they say have disrupted their daily lives and clogged public transport.

Britain's foreign secretary on Thursday said Hong Kong could still take a "meaningful step" towards democracy after mass protests posed the most serious test to the city's stability since its handover to China.

Hundreds of thousands of people took to Hong Kong's streets to call for fully free leadership elections late last year, paralyzing parts of the city for more than two months.

Hong Kong's pro-Beijing leader has told residents in his Lunar New Year address to be "inspired" by this year's zodiac animal -- the sheep -- after anti-government protests paralyzed parts of the city.

Chief Executive Leung Chun-ying encouraged residents to "take inspiration" from the sheep, describing the zodiac ungulates as "mild and gentle animals living peacefully in groups".

A Hong Kong boat captain was on Monday sentenced to eight years in prison for the manslaughter of 39 people in a 2012 ferry collision, the city's worst maritime disaster in nearly four decades.

Sea Smooth skipper Lai Sai Ming, 56, was found guilty on Saturday following a trial that gripped the city, over the accident between his high-speed ferry and a pleasure boat near Lamma Island.

Hong Kong police fired pepper spray and arrested protesters demonstrating against an influx of visitors from mainland China inside a shopping mall Sunday, reports said.

More than 100 people took part in the protest in the town of Tuen Mun in the New Territories, not far from one of the border crossings to the mainland.

Thousands of pro-democracy protesters took to the streets of Hong Kong Sunday for the first time since mass demonstrations shut down parts of the city for more than two months.

A sea of yellow umbrellas -- the symbol of the campaign -- moved slowly through central Hong Kong with crowds shouting for "true universal suffrage".

Hong Kong pro-democracy newspaper tycoon Jimmy Lai was arrested and released by police Wednesday after turning himself in, the latest figure targeted in a broadening investigation which protest leaders describe as harassment.

Tension remains high in the semi-autonomous southern Chinese city after more than two months of street blockades by demonstrators seeking free leadership elections. Lai's home and office were firebombed last week and he was also targeted during the protests.

Hong Kong student leader Alex Chow on Sunday accused police of mounting a campaign of harassment against pro-democracy campaigners after he became the latest figure to be arrested and released by police.

Several protest leaders have been summoned in recent days over offenses relating to the mass protests that shut down parts of the city late last year, only to be released in what lawyers have condemned as a potential abuse of process.

Physical assaults and cyber attacks are part of the "increasing risk" to media in Hong Kong, a city which prides itself on free expression compared with strict censorship in mainland China, a report said Friday.

Published by U.S. literary and human rights group PEN American Center, the report comes as tensions remain high after more than two months of mass protests for fully free leadership elections ended in December with no concessions on reform.