Thousands of police have been deployed across Hong Kong as a top-ranked Beijing official addressed an economic summit.
Tensions were high amid calls for greater autonomy in the Chinese special administrative territory.
Protesters took to the streets of Hong Kong, marching towards a major summit attended by top Chinese official Zhang Dejiang.
He was speaking at a conference on the "One Belt, One Road" initiative -- President Xi Jinping's signature plan to build roads, railways, ports and pipelines across Asia and Europe.
Mr Dejiang is the third-most powerful member of Chinas ruling Politburo and manages Hong Kong and Macau Affairs for the government.
And he is the highest-ranking official to arrive in Hong Kong since the mass protests of 2014.
This man was among those who hoped to use the visit to get across concern about Hong Kong's relationship with the mainland government.
"We are out here to show the Beijing leaders what kind of change people are looking for."
Some activist clinched yellow umbrellas, a symbol used in demonstrations that two years ago overtook Hong Kong streets, calling for electoral change.
Zhang Dejiang's presence appears to have reignited those tensions.
Around 6,000 Hong Kong police officers have been deployed to maintain order -- barriers put up and bricks glued to the ground.
This man says he's worried his message for Mr Dejiang was muted by the tight security.
"He was well protected by the police and nobody can even come close to him. We urge, we want to let him listen to the voice of the Hong Kong people."
It was a fairly peaceful demonstration in the end, apart from what appeared to be a tense face-off between pro- and anti-mainland government voices.
Police positioned themselves between the two sides.
Meanwhile, inside the summit, Zhang Dejiang was pledging to strengthen Hong Kong's business efforts and co-operation with the mainland.
"We will support Hong Kong in building on its existing strengths and exploring new advantages, support closer exchange and cooperation between Hong Kong and the mainland."
Some of the demonstrators also raised allegations of China's human rights abuses and what they say are government efforts to limit Hong Kong's authority.
Others were frustrated over issues such as press freedom and freedom of speech.
Zhang Dejiang is expected to meet local politicians and visit a public housing estate before he returns to Beijing.
