China is preparing for a highly-choreographed anniversary celebration on October 1

Chinese President Xi Jinping vowed Monday to uphold the "one country, two systems" principle in Hong Kong, after months of pro-democracy protests in the semi-autonomous city.

Speaking at a reception in Beijing the night before celebrations to mark the country's 70th anniversary, President Xi said the country would "continue to fully and faithfully implement the principles of 'one country, two systems'" and a "high degree of autonomy."

Hong Kong has been plagued by months of unrest over what protesters say are eroding freedoms in the financial hub, which was handed back to China by Britain in 1997.

"We are confident that with the full backing of the motherland and the concerted efforts of our fellow Chinese in Hong Kong and Macau who love the motherland... (Hong Kong) will prosper and progress alongside the mainland," President Xi said.

China is preparing for a highly-choreographed anniversary celebration on October 1, including a huge military parade and anniversary gala.

Protesters in Hong Kong are hoping to upstage the event with another demonstration on Tuesday following a weekend of intense clashes with police.

Beijing has been positioning the event as a triumphant celebration of its economic growth over the last seven decades, as well as emphasising the importance of a unified territory and nationalism.

"Unity is iron and steel. Unity is a source of strength," President Xi said in his speech.

He also referred to the self-ruled island of Taiwan, which Beijing still sees as part of its territory awaiting reunification.

"The complete reunification of the motherland is an inevitable trend... no one and no force can ever stop it," he said.