A helicopter with a Chinese flag flies past during a flag-raising ceremony marking the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Fishing vessels sail with Chinese and Hong Kong flags to celebrate the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Police stand guard at Causeway Bay after authorities denied permission for a protest rally during the 24th anniversary of the former British colony’s return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Police stand guard at a public hospital where a man was sent after allegedly stabbing a police officer in Causeway Bay, during the 24th anniversary of the former British colony's return to Chinese rule and on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

A pro-China supporter holds a Chinese flag to celebrate the 24th anniversary of the former British colony’s return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Police officers block Victoria Park after denied permission for a protest rally during the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Blocked road at Causeway Bay after police denied permission for a protest rally during the 24th anniversary of the former British colony’s return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

A woman raises her hands in a symbol of "Five demands, not one less" at Causeway Bay after police denied permission for a protest rally during the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Police try to disperse media and pro-democracy supporters after authorities denied permission for a protest rally during the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Chief Secretary for Administration John Lee Ka-chiu and guests attend the flag-raising ceremony marking the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

The Chinese national flag is seen during morning assembly at a secondary school, marking the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

A pro-democracy protester with Union flag is taken by police at Causeway Bay after police denied permission for a protest rally during the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

A policeman takes pictures at the site where a man allegedly stabbed a police officer in Causeway Bay, during the 24th anniversary of the former British colony's return to Chinese rule and on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

A pro-democracy protester with a Union flag mask is taken by police at Causeway Bay after police denied permission for a protest rally during the 24th anniversary of the former British colony’s return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Pro-China supporters hold Chinese flags to celebrate the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Police officers block Victoria Park after denied permission for a protest rally during the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Students take a picture with the People's Liberation Army during morning assembly at a secondary school, marking the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Police officers raise Chinese and Hong Kong flags during a flag-raising ceremony marking the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Police officers walk past Victoria Park on the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.

Police raise a warning banner at Causeway Bay after authorities denied permission for a protest rally during the 24th anniversary of the former British colony's return to Chinese rule, on the 100th founding anniversary of the Communist Party of China, in Hong Kong, China July 1, 2021.