Hong Kong: China's number three official Mr Zhang Dejiang has said Beijing was aware of problems in Hong Kong but would respect the special administrative region's autonomy as protesters hit the streets to oppose Chinese attempts to squeeze local freedoms.

Mr Zhang's visit to Hong Kong on Wednesday, which comes at a time of mounting political tensions in the region, is the first by a senior state leader since tens of thousands of people mounted a massive but ultimately unsuccessful push to pressure Beijing to grant full democracy during the 'Occupy Central' street protests in late 2014.

Supporters of Zhang Dejiang, the chairman of China's National People's Congress, at a rally in Hong Kong on Wednesday. Credit:Getty Images

Thousands of police were deployed across Hong Kong, preventing protesters from coming near Mr Zhang as he toured a science park and a harbourfront exhibition centre where he addressed an economic summit.