Xi warns Hong Kong of crossing 'red line' by challenging Beijing

China's President Xi Jinping has warned the people of Hong Kong not "to challenge the power of the central government" as it will be considered an act of crossing a red line which is "absolutely impermissible," as the former British colony marked 20 years of Chinese rule on Saturday.

His warming comes at a time when huge protests are seen where activists are calling for self-determination or even full independence for Hong Kong, which has infuriated Beijing.

He added that Hong Kong had "more extensive democratic rights and freedoms than at any other time in its history."

"Any attempt to endanger China's sovereignty and security, challenge the power of the central government and the authority of the Basic Law of the Hong Kong Special Administrative Region, or use Hong Kong for infiltration or sabotage activities against the mainland, is an act that crosses the red line and is absolutely impermissible", Xi said, emphasizing Beijing's control over the city, now a special administrative region of China.

It's Xi's first visit to the city since he took power in Beijing in 2013, and comes amid fears by some Hong Kongers of increasing Chinese encroachment on the city's autonomy -- guaranteed under a framework known as "one country, two systems."

Xi's warning came as pro and anti-Beijing protesters clashed amid the swearing of ceremony of Hong Kong's first female Chief Executive Leader Carrie Lam.Lam is being considered by critics as a China stooge in a city where HongKongers fears of Beijing's tightening grip on the city's autonomy and freedoms of nearly eight million people.

Protesters tried to disrupt the flag-raising ceremony, but were prevented by the heavy deployment of troops and huge police cordon.

Activisits, including high-profile campaigner Joshua Wong were detained and bundled into police vans as their supporters shouted "shame." He was later released.