On the anniversary of Hong Kong's return to China officials reiterated the importance of following national security laws. Officials said Friday they will enforce the law to halt all pro-democracy rallies.

Hong Kong police sealed off Victoria Park - the site where pro-democracy activists gather annually to protest the handover. Police put up billboards warning people they faced prosecution if they gathered in the area.

There was a heavy police presence along Hong Kong's Causeway Bay shopping district. Police arrested pro-democracy activist Alexandra Wong - also known as Grandma Wong - who was waving a British flag.

In a Facebook post, Hong Kong police said they arrested 19 people suspected of possessing weapons and imitation firearms, distributing seditious publications, disorderly conduct and desecrating the national flag.  

Police said they had received reports some groups were encouraging people online to take part in a protest. Under the national security law, implemented last year, protests and mass gatherings deemed a danger to national security are illegal and punishable.

The law, which was drafted by the China government, was passed in response to a wave of anti-government protests in 2019. Critics said it was a violation of China's promise to keep Hong Kong autonomous for at least 50 years.

Hong Kong Chief Secretary John Lee said national security doesn't violate human rights. The law respects everyone's rights and freedoms of the press and assembly. Lee said the law helped restore Hong Kong's social and political stability.

"Our team has more confidence than ever in Hong Kong's prospects. In the coming year, we will continue to uphold national security with determination and improve the implementation of the 'one country, two systems principle,'" Lee said.

Authorities have arrested dozens of democracy activists and journalists. Demonstrations have been banned and the government has denied groups from holding the annual June 4 Tiananmen Square candlelight vigil for two consecutive years.