Hong Kong democracy advocates expressed alarm Friday after Chinese army vehicles were photographed travelling down a major thoroughfare, in what they condemned as a show of "military might" ahead of expected protests.

At least four People's Liberation Army (PLA) armored personnel carriers were seen in the small hours of Thursday near the busy Jordan and Yau Ma Tei regions of the city, the Apple Daily newspaper reported.   

Thousands protested in Hong Kong Sunday against plans by pro-democracy activists to paralyze the city center with a mass sit-in unless China grants acceptable electoral reforms.

Public discontent in the semi-autonomous Chinese city is at its highest for years, with concern at perceived interference by Beijing and growing divisions over how Hong Kong's leader should be chosen in 2017 under the planned reforms.

The Hong Kong Law Society has sent a strong rebuke to Beijing after it passed a vote of no confidence in its own president, who backed a controversial white paper reaffirming China's control over the city.

Hong Kong's leader declared a planned occupation of the city's financial district by pro-democracy campaigners illegal Tuesday, and warned senior officials not to support the movement.

Public discontent in Hong Kong is at its highest for years, with heightened concern over perceived interference from China, notably Beijing's insistence that it vet candidates before the vote for the city's next leader in 2017.

Leading Hong Kong pro-democracy activists on Wednesday urged former colonial power Britain not to turn a blind eye to "attacks" on freedoms that were enshrined in the 1997 handover to China.

Former Hong Kong number two official Anson Chan and campaigner Martin Lee said the semi-autonomous city risked becoming "ungovernable" just over two weeks after half a million people marched in Hong Kong demanding reforms.

China on Wednesday accused London of interfering in its internal affairs after British Deputy Prime Minister Nick Clegg met two leading Hong Kong pro-democracy activists urging greater freedoms from Beijing.

China "lodged solemn protests" with Britain over Tuesday's meetings with Martin Lee, founder of Hong Kong's opposition Democratic Party, and Anson Chan, the former number two in the city's government, the official Xinhua news agency reported.

Pro-democracy lawmakers in Hong Kong hit back Friday at former colonial ruler Britain over a report they said showed no "commitment" to the city and strived to avoid embarrassing Beijing.

The British parliamentary report comes as tensions rise over complaints of increasing interference from China in the semi-autonomous city, and Beijing's insistence that it vet candidates for Hong Kong's next leader in 2017.

Police on Friday arrested the organizers of Hong Kong's biggest pro-democracy rally since the city was handed back to China, sparking outrage from campaigners who denounced the "political suppression".

Five members of the Civil Human Rights Front, including its convener, were arrested three days after the march, which the group said mobilized half a million people to voice anger at Beijing's ever-tightening grip on Hong Kong.

Hong Kong police arrested more than 500 protesters at a sit-in early Wednesday following a huge pro-democracy rally that organizers said mobilized half a million people demanding the right to choose their next leader.

The arrests came at the end of a largely peaceful rally on Tuesday that protest leaders said brought the biggest crowds onto the streets since the city was handed over from Britain to China in 1997.

Hundreds of thousands of protesters, some waving colonial-era flags and chanting anti-Beijing slogans, staged a pro-democracy march in rain-soaked Hong Kong Tuesday that organizers say could be the largest since the city was handed back to China.

The scale of the turnout reflects surging discontent over Beijing's insistence that it vet candidates before a vote in 2017 for the semi-autonomous city's next leader.