Police detain a protester after spraying pepper spray during a protest in Causeway Bay before the annual handover march in Hong Kong, Wednesday, July. 1, 2020. Hong Kong marked the 23rd anniversary of its handover to China in 1997, and just one day after China enacted a national security law that cracks down on protests in the territory. (AP Photo/Vincent Yu)

HONG KONG (AP) — Hong Kong police made the first arrests Wednesday under a new national security law imposed by China’s central government, as thousands of people defied tear gas and pepper pellets to protest against the contentious move on the anniversary of the former British colony’s handover to Chinese rule.

Police said 10 people were arrested under the law, including a man with a Hong Kong independence flag and a woman holding a sign displaying the British flag and calling for Hong Kong’s independence — all violations of the law that took effect Tuesday night. Others were detained for possessing items advocating independence.

Hong Kong police said on Facebook that they arrested some 370 people on various charges, including unlawful assembly, possession of weapons and violating the new law, which was imposed in a move seen as Beijing’s boldest step yet to erase the legal firewall between the semi-autonomous territory and the mainland’s authoritarian Communist Party system.

The law, imposed following anti-government protests in Hong Kong last year, makes secessionist, subversive, or terrorist activities illegal, as well as foreign intervention in the city’s internal affairs. Any person taking part in activities such as shouting slogans or holding up banners and flags calling for the city’s independence is violating the law regardless of whether violence is used.

The most serious offenders, such as those deemed to be masterminds behind these activities, could receive a maximum punishment of life imprisonment. Lesser offenders could receive jail terms of up to three years, short-term detention or restriction.

Wednesday’s arrests came as thousands took to the streets on the 23rd anniversary of Britain’s handover of Hong Kong to China in 1997. For the first time, police banned this year’s annual march. Protesters shouted slogans, lambasted police and held up signs condemning the Chinese government and the new security law.

Some protesters set fires in Hong Kong’s trendy shopping district, Causeway Bay, while others pulled bricks from sidewalks and scattered obstacles across roads in an attempt to obstruct traffic. To disperse protesters, police shot pepper spray and pepper balls, as well as deployed water cannons and tear gas throughout the day.

Hong Kong’s leader strongly endorsed the new law in a speech marking the anniversary of the handover of the territory — officially called the Hong Kong Special Administrative Region.

“The enactment of the national law is regarded as the most significant development in the relationship between the central authorities and the HKSAR since Hong Kong’s return to the motherland,” chief executive Carrie Lam said in a speech, following a flag-raising ceremony and the playing of China’s national anthem.

“It is also an essential and timely decision for restoring stability in Hong Kong,” she said.

A pro-democracy political party, The League of Social Democrats, organized a protest march during the flag-raising ceremony.