Protesters rally in Hong Kong on handover anniversary

But a Hong Kong bookseller who was detained and interrogated for months in mainland China, and was due to lead the annual march, pulled out at the last minute citing a "serious threat" to his security.

Tensions are high in the southern Chinese city after the explosive revelations by Lam Wing-kee, whose account of his detention on the mainland after he went missing last year sent shockwaves through a city where residents are worried of eroding freedoms.

The 61-year-old was one of five employees of a Hong Kong firm that published salacious titles about leading Chinese politicians and who disappeared only to resurface over the border.

His story fanned growing concerns that Beijing is increasing its influence in semi-autonomous Hong Kong, which is ruled under a "one country, two systems" deal enshrined in the July 1997 handover agreement, guaranteeing its freedoms and way of life for 50 years.

"Lam Wing Kee is facing a serious threat and is forced to not attend the rally," said protest leader Lau Shan-Ching, who spent 10 years in a Chinese jail as a prisoner of conscience.

The march organisers said Lam had pulled out because he had been tailed in recent days.

"He had observed that he had been followed by strangers in the last two days. He got greatly annoyed about his personal safety so he decided not to come today," pro-democracy lawmaker Albert Ho told reporters.

"Mr Lam has reason to be scared that this may be people from the mainland," Ho added.

The march got underway nonetheless at around 3:30 pm (0730 GMT) from the city's Victoria Park, with the front protesters holding a huge banner that read "Stand in Unity. Protect Hong Kong".

"We want to choose our own government," shouted protesters, some of whom carried yellow umbrellas -- a symbol of the pro-democracy movement that brought parts of the city to a standstill for months in 2014.

Anger, disappointment

"As a Hongkonger, I feel I need to speak out for the city. To pursue democracy is the issue this generation is most concerned about," rally participant Eva Li, 20, told AFP.

Jackie Hung, a member of pro-democracy Civil Human Rights Front, said the city's unpopular leader Leung Chun-ying should resign.

"(Hong Kong people) are angry with the current government and very disappointed at how things are managed," she told AFP.

The turnout at the beginning of the march appeared lower than the organiser's predictions of 100,000, but it was expected to gather pace as it snaked through the city.

A sense of impotence clouded last year's rally after the 2014 protests failed to win political reform and the turnout was low.

But there are growing calls in the city to take a different path in demanding more rights, particularly from groups like the emerging "localist" movement, which is seeking independence from China.

Some are now demanding a return to British rule as a stepping stone towards independence, while others say violence may be necessary to bring change.

Following the main march, several pro-independence groups are due to gather outside China's liaison office in a protest seen as a possible flashpoint.

Participants have said they will wear black clothes and masks. A poster advertising the rally showed mocked-up demonstrators wearing motorcycle helmets and carrying sticks.

Police have already warned they will take "resolute and effective actions against illegal acts" and say the pro-independence protesters have not asked for required permission for their rally.

Leung stopped short of speaking about the rallies Friday morning during an official celebration of the handover, but asked Hongkongers to be "united".