Several hundred thousand people have been taking part in a march in Hong Kong to protest against the introduction of a new anti-subversion law.
Protesters say the new law will curb their freedoms
The organisers say up to 400,000 people have taken part, but that figure has not yet been confirmed by the authorities.
Many demonstrators are angry at new national security legislation - due to be introduced next week - which they say is a threat to political, religious and media freedoms.
But a whole range of issues were being protested against, from the dire state of the territory's economy, to the government's handling of the deadly Sars virus.
The protest overshadowed the official celebrations to mark the sixth anniversary of Hong Kong's return to Chinese control, presided over by Chinese Prime Minister Wen Jiabao.
One group of protesters burned the Chinese Communist Party flag as Mr Wen desperately tried to reassure reporters that Article 23 would not infringe on the considerable autonomy the territory has been promised.
It "absolutely will not affect the different rights and freedoms that Hong Kong people - including reporters - enjoy under the law", Mr Wen said.
Mr Wen left Hong Kong before the organised protest started.
"Return rule to the people," chanted protesters dressed in black to mourn what they said was the demise of rights and freedoms in the once free-wheeling territory.
Outlaws: Reporting state "secrets"
Criticism of Beijing authority
Access to "subversive" material
Threatens: Currently legal groups, such as Falun Gong
Many groups were represented, with members of the Falun Gong spiritual movement in their distinctive yellow T-shirts and Christian groups strumming guitars.
"The government is trying to use the law to suppress
people's views and voices," lawyer Terry Chan told Reuters news agency.
"Tung's government is a malignant tumour on society...If we
let this fester, Hong Kong will die," she said.
"This will push Hong Kong toward an era of tyranny,"
said WC Mak, a 74-year-old retired nurse.
Our correspondent, who was with the demonstrators, says that although the atmosphere was peaceful, there was no mistaking the strength of feeling.
The controversial bill - Article 23 - is due to be signed into law next week.
It states that Hong Kong must enact laws to prohibit "treason, secession, sedition and subversion against China or theft of state secrets, to prohibit foreign political organisations or bodies from conducting political activities in the region, and to prohibit political organisations or bodies of the region from establishing ties with foreign political organisations or bodies."
Article 23 is being proposed as part of the Basic Law governing Hong Kong, which was negotiated by China and Britain.
Wen Jiabao was in Hong Kong for the anniversary of the handover
But Britain and the European Union have also criticised the bill, saying it could compromise the territory's autonomy from mainland China.
Hong Kong officials reject the criticism.
"The fear that freedoms will be threatened are actually totally unfounded," Hong Kong's Security Secretary Regina Ip told the BBC's World Today programme.
At the anniversary celebrations earlier on Tuesday, Mr Wen watched as the five-starred Chinese national flag and the red Bauhinia flower flag of Hong Kong were raised.
Helicopters swirled overhead and patrol boats sprayed jets of water in what was a deliberate echo of the ceremony in 1997, when Britain's union flag was finally lowered.
Mr Wen then left for Beijing, where he was due to take part in celebrations marking the 82nd anniversary of the founding of the Chinese Communist Party.