Hong Kong lawmakers passed a controversial bill giving mainland authorities joint control over a new rail terminus Thursday despite angry protests the move would erode the city's autonomy from Beijing.
It is illegal for mainland law enforcement to operate in semi-autonomous Hong Kong under the city's mini-constitution, the Basic Law.
But with a high-speed rail link to Hong Kong's neighbouring mainland cities of Shenzhen and Guangzhou due to open this year, plans have now been approved for a joint immigration checkpoint which will see mainland officials stationed in a new terminus in the heart of Hong Kong.
Long-running opposition against the proposals reached a head Thursday evening, with about 200 people demonstrating outside the Legislative Council against the bill.
"The Basic Law can no more provide protection to Hong Kong people. Our freedom is in danger," said one pensioner who gave his surname as Wong.
Hong Kong enjoys liberties unseen on the mainland including freedom of speech and an independent judiciary, with the rule of law a bedrock of its culture and business success.
The joint immigration arrangement bill was pushed through by Hong Kong's partially elected legislature, after the council president kicked out several pro-democracy lawmakers who protested. They were later barred from chamber.
Holding up slogans during a debate ahead of the vote, angry opposition lawmakers accused the president of "crippling the legislature" and ceding Hong Kong to the mainland.
"There's been every sign that the legislative and the executive branches are conniving together to sell out Hong Kong lock, stock and barrel," said pro-democracy lawmaker Claudia Mo.
Concerns of Chinese operatives working undercover in Hong Kong has mounted after the alleged abductions of a city bookseller and a reclusive mainland businessman in recent years.
The troubled HK$84.4 billion ($10.7 billion) high-speed rail link is one of a number of huge cross-border infrastructure projects approaching completion as concern grows Beijing is tightening its grip on the city.