Image copyright AP Image caption Organisers said they estimated 110,000 people attended - but the police estimate was far lower

Tens of thousands of protesters have attended an annual pro-democracy march in Hong Kong.

Protesters held photos of Lam Wing Kee, one of five booksellers who went missing last year after publishing books critical of China's leaders.

Mr Lam returned to Hong Kong in June, saying he had been detained in the mainland for eight months.

He was due to lead Friday's march but dropped out, reportedly over fears for his personal safety.

The case of the booksellers raised international concerns that Hong Kong's judicial independence and freedom of speech were being eroded.

Image copyright EPA Image caption Lam Wing Kee pulled out of the march over fears for his safety

Media playback is unsupported on your device Media caption Albert Ho: "He (Lam Wing Kee) became increasingly worried about his personal safety"

Albert Ho, a lawmaker who has been advising 61-year-old Mr Lam, told the BBC: "He feels he is under intense surveillance."

"He has been physically followed by unknown people. He is under intense pressure."

Mr Ho added that arrangements were being made for Mr Lam to go to a safe house.

Image copyright AFP Image caption Many in the city want the Chief Executive CY Leung to step down

China and the booksellers

1. Lui Bo, general manager. Went missing: Shenzhen, 15 October 2015 Returned: March 2016

2. Cheung Jiping, business manager. Went missing: Dongguan, 15 October Returned: March 2016

3. Gui Minhai, co-owner. Went missing: Thailand, 17 October Still in mainland China

4. Lam Wing-kee, manager. Went missing: Shenzhen, 23 October Returned: June 2016

5. Lee Po, shareholder. Went missing: Hong Kong, 30 December Returned: March 2016

'Black-mask rally'

The 1 July march marks 19 years since the territory's handover from Britain to China.

Organisers said 110,000 people attended the march, while police said there were 19,300 demonstrators at the peak of the protest.

Marchers also called for the resignation of Chief Executive CY Leung, who has faced criticism for what protesters say was a failure to protect the booksellers.

Image copyright ANTHONY WALLACE Image caption The 1 July march marks 19 years since the city's handover from Britain to China

"The fact that he [Lam Wing Kee] and others were so blatantly made disappeared should be an alarm for everyone in Hong Kong," Billy Leung, a charity worker told the Associated Press.

"If you have a critical mind and you start criticising what you think is not correct and not right, it could very well be you next time."

Another participant, Eva Li, told AFP: "I need to speak out for the city. To pursue democracy is the issue this generation is most concerned about."

A government spokesman said they note "different views on policies and initiatives" but also hoped everyone would "strive to seek common ground".

Image copyright EPA Image caption Some activists called for independence from China

Meanwhile, hundreds of police officers guarded China's liaison office in Hong Kong, after localist groups said they would hold a separate pro-independence "black-mask" rally there.

What are Hong Kong's localists angry about?

Police said that the pro-independence protests had not asked for required permission and warned that they would take "resolute and effective actions" against illegal acts.

Last year's anniversary democracy rally saw an estimated 48,000 people take part, with police placing the number at 20,000.