Hong Kong police make their first arrests under a new "anti-protest" law imposed by Beijing
The legislation comes into effect as the city marks 23 years since the end of British rule
Police fire water cannon and detain hundreds of people at demonstrations marking the anniversary
The new security law targets secession, subversion and terrorism with punishments up to life in prison
Critics say it erodes freedoms that were meant to be guaranteed by China for at least 50 years from 1997
China rejects criticism from foreign countries, saying it will not allow interference in its domestic affairs
Up to three million Hong Kong residents are to be offered the chance to settle in the UK
UK Foreign Secretary Dominic Raab said the new security law constituted a "clear violation" of the autonomy of Hong Kong and was a "clear and serious violation" of the treaty drawn up between the UK and China.
He told reporters in London that China had not lived up the promises it made to the people of Hong Kong.
When Hong Kong was handed back to China on 1 July 1997, following more than 150 years of British control, the "one country, two systems" principle was established as the foundation of the relationship.
While Hong Kong is part of China, the policy has given the Special Administrative Region (SAR) a high degree of autonomy.
This principle of "one country, two systems" is enshrined in a document called the Basic Law - Hong Kong's mini-constitution. It protects rights such as freedom of assembly and freedom of speech - neither of which exist in mainland China - and also sets out the structure of governance for the territory.
But politically China still holds control over Hong Kong. The National People's Congress Standing Committee (NPCSC) - China's rubber-stamp parliament - holds the ultimate "power of interpretation" of the law. Beijing must also approve the chief executive appointment and controls Hong Kong's defence and foreign affairs.
The freedoms enshrined under the Basic Law expire in 2047 and it is not clear what Hong Kong's status will be after that. But critics of China's new national security law say it undermines the region's freedoms and marks "the end of Hong Kong".
Michael Bristow
BBC World Service Asia Pacific editor
The law gives Beijing extensive powers to shape life in the territory that it has never had before. It not only introduces a series of tough punishments for a long list of crimes, it changes the way justice is administered.
Trials can be held in secret - and without a jury. Judges can be handpicked. The law reverses a presumption that suspects will be granted bail. There appears to be no time limit on how long people can be held.
Crimes are described in vague terms, leading to the possibility of broad interpretation, and the right to interpret exists only in Beijing. Foreign nationals outside of Hong Kong face prosecution.
Most cases will be handled in Hong Kong, but the mainland can take over "complex", "serious" or "difficult" cases. Whether or not you think the legislation was necessary, it is impossible to deny its significance. As Hong Kong's leader Carrie Lam put it: this is a turning point.
In May, China proposed a wide-ranging new security law for Hong Kong which would make it easier to punish protesters and would reduce the city's autonomy.
Details of the law were kept secret until it was unanimously passed by China's National People's Congress Standing Committee on 30 June and came into force later that day.
Under its terms, crimes of secession, subversion, terrorism and collusion with foreign forces are punishable by a minimum jail sentence of three years, with the maximum being life.
It also says:
Beijing will also have power over how the law should be interpreted, and not any Hong Kong judicial or policy body. If the law conflicts with any Hong Kong law, the Beijing law takes priority.
Image source, ReutersHello and welcome to our live coverage of fresh protests in Hong Kong after China imposed a new security law on the territory.
Here is a summary of key developments so far: