China has accused Hong Kong democracy activists of trying to start a revolution as it warned some campaigning for recent primaries may have breached a tough new security law it imposed on the city.

The bellicose comments by the Liaison Office, which represents China's government in the semi-autonomous city, dramatically heighten the risk of prosecution for opposition parties and leading figures.

More than 600,000 Hong Kongers turned out over the weekend to choose candidates for upcoming legislative elections despite warnings from government officials that the exercise could breach Beijing's sweeping new law.

Polls for the city's partially elected legislature are due to take place in September.

Pro-democracy parties are keen to use seething public anger towards Beijing's increasingly authoritarian rule to win a majority within a chamber that has always been weighted in favour of pro-establishment parties.

Control could give them a greater ability to stall budgets and legislation, one of the few tactics left open to the opposition camp.

But in a statement released late Monday, the Liaison Office described the primaries as "a serious provocation against the current election system".

It said campaigning that pushed to take control of and paralyse the chamber is a breach of Article 22 of the security law.

Article 22 targets "subverting state power". It outlaws "serious interference and obstruction" of the central and Hong Kong governments, or any act that causes them to be "unable to perform their functions normally".