By Venus Wu
HONG KONG (Reuters) - Thousands of Hong Kong residents marched in protest on the 19th anniversary of the financial hub's return to Chinese rule on Friday as tensions simmer against Chinese authorities over the abductions of several Hong Kong booksellers.
Some waved banners criticizing Beijing for the cross-border abductions as acts of a "totalitarian" regime, as well as calling for the release of leading dissidents.
"This is a very grave threat to the safety of Hong Kong residents that an unknown force is spying on people," said pro-democracy lawmaker Cyd Ho at the rally.
"The Hong Kong government has to follow up with the central government on what's really happening behind the scenes."
The city has been unnerved over the past year by the disappearances of five booksellers who specialized in works critical of Chinese leaders. One of the men, Lam Wing-kee, who was detained for eight months by Chinese agents and released last month, criticized Beijing for "violating Hong Kong's rights" through illegal cross-border enforcement operations.
The tactics have raised fears of Communist Party rulers in Beijing eroding the so-called "one country, two systems" formula, granting Hong Kong a high degree of freedom and autonomy since its 1997 return from British to Chinese rule.
China has denied wrongdoing.
Lam, who had been due to lead the July 1 march that each year draws thousands, pulled out, citing safety concerns after being followed by two unknown strangers, a lawmaker said.
"He feels increasingly concerned about his own personal safety," said pro-democracy lawmaker Albert Ho.
A senior Chinese official, Wang Guangya, who heads the Hong Kong and Macau Affairs Office in Beijing, said the booksellers had "destroyed" the one country, two systems formula by publishing banned books in mainland China.
Chinese President Xi Jinping, however, said in a speech on Friday that "no matter what the difficulties and challenges, our confidence and determination towards one country, two systems will not waver".
Xi added Hong Kong would continue to enjoy a high degree of autonomy and Beijing would strictly adhere to the law.
The July 1 protests are considered a barometer of public sentiment towards Beijing ahead of citywide legislative elections in September.
A group of activists who advocate Hong Kong independence from China are planning an evening "black mask" protest outside China's main representative "Liaison Office".
A 79-day "umbrella revolution" in late 2014 demanding Beijing allow full democracy in Hong Kong brought chaos to the streets.
(Additional reporting by Lindsy Long, Sharon Shi and Hera Poon in Hong Kong and Ben Blanchard in Beijing; Writing by James Pomfret; Editing by Nick Macfie)