Chinese president Hu Jintao is in Hong Kong to install a new but already unpopular governor of the semi-autonomous Chinese territory.
It is an event that has become a magnet for public disaffection about Hong Kong's widening gap between rich and poor and lack of democracy.
Large-scale protests are planned for Sunday's swearing-in of Leung Chun-ying.
His popularity has tumbled since he was chosen in March because of a scandal over illegal additions to his mansion and persistent fears that he is an underground Communist Party member.
Security was extremely tight as Mr Hu arrived to oversee the ceremony and mark the 15th anniversary since China resumed control of the former British colony.