Hong Kong has launched one if its largest security operations in years, as a high-ranking Chinese politician is set to arrive in the city.
Zhang Dejiang, the man responsible for Hong Kong affairs in Beijing, arrives amid concerns over the territory's freedoms and interference by China.
More than 6,000 police have been deployed and restricted zones imposed in the city centre, local media report.
Pro-democracy groups say they will stage protests during the visit.
Mr Zhang, who is also the chairman of the National People's Congress Standing Committee, is the most senior official to visit Hong Kong since 2014 when thousands of protesters took over major parts of the city to demand fully free elections.
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Since then so-called "localist" groups have sprung up and shown themselves willing to use violence to battle what they see as a dilution of the city's identity, fearing growing social and political influence from mainland China.
In February, hundreds of demonstrators, fuelled by such localist sentiment, dug up and threw bricks during a violent clash with police as they tried to shut a night food market - seen by protesters as a symbol of local traditions.
Earlier this month, reports said paving stones had been reinforced with glue around the legislative building so that they could not be used as projectiles.
Local media also report that police have been stationed on Hong Kong's iconic Lion Rock mountain in an effort to prevent the practice of anti-Beijing banners being unfurled from there.