China has sent a pre-dawn convoy of tanks and troops into the streets of Hong Kong as pro-democracy protesters plan for another big weekend of action.

Chinese state media shared pictures of armed personnel carriers and trucks carrying troops at the border early on Thursday morning, though it was unclear if they were entering or leaving Hong Kong.

It also showed a picture of a small naval vessel arriving in Hong Kong.

Later the state-run news agency Xinhua released a report describing the move as routine.

Asian and Western diplomats in Hong Kong watching the movements of the People’s Liberation Army had been expecting a routine rotation about this time and were be looking closely for any sign of increased numbers or unusual activity.

“The Hong Kong Garrison of the Chinese People’s Liberation Army conducted the 22nd rotation of its members in the wee hours of Thursday since it began garrisoning Hong Kong in 1997,” the official Xinhua news agency said.

“Approved by the Central Military Commission, the move is normal routine annual rotation in line with the Law of the People’s Republic of China on Garrisoning the Hong Kong Special Administrative Region, which stipulates that ‘the Hong Kong Garrison shall practise a system of rotation of its members’.”

But pro-democracy Hong Kong politician Dennis Kwok said the PLA troop movements were deliberate posturing by Beijing and an attempt to warn people.

“I don’t believe that, given the sensitive timing that we have right now, that this is anything routine,” he said.

“I believe it’s a deliberate posture on the part of the PLA to tell, or warn, the Hong Kong people that they may be deployed.”

Mr Kwok said the use of troops would be the end of Hong Kong and he warned the government in Beijing against any such move.

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Wednesday’s troop movements come before a major anti-government rally planned for Saturday, as Hong Kong nears its third month of mass protests.

The angry and sometimes violent protests against the government have lasted throughout the former British colony’s summer, sparked by a now-suspended extradition bill and concerns that Beijing was trying to bring the territory under greater mainland control.

The rotation included a small naval vessel, seen here arriving at Stonecutters Island Naval Base. Photo: Xinhua News Agency

The protests are the greatest political threat to Hong Kong’s government since the territory returned to Chinese rule in 1997, and one of the biggest popular challenges to Chinese leader Xi Jinping since he came to power in 2012.

Earlier in August, photos emerged of Chinese troops and equipment massing at a sports stadium in Shenzhen, a city bordering Hong Kong.

Footage from Xinhua also further showed the army undertaking military exercises.

It was estimated dozens of armoured vehicles and thousands of troops had congregated to warn of a looming Chinese government intervention in Hong Kong.

-with AAP