The arrests came on Thursday, when the Hong Kong government held a celebration, reports NKK.

Police told NHK the 19 are suspected of desecrating China's national flag and holding placards that incite secession.

Protest marches were banned this year as they were a year ago. Before the ban, tens of thousands of people rallied on the anniversary every year since 2003, the news portal reported.

Hong Kong, a former British colony, was handed over to China in 1997, and the Basic Law preserves its autonomy as a Special Administrative Region under the principle of “one country, two systems”.