Trains and buses will be diverted due to the annual march today, the July 1 anniversary of the city's handover to China. The main march, organised by the Civil Human Rights front is expected to start at 3pm from Victoria Park and protesters will march to government headquarters at Tamar in Admiralty.
Two previous protests on June 9 and 16 drew more than a million marchers on each occasion.
Roads may also be affected by flash protests around government headquarters in Admiralty before and after the march.
The MTR company is expected to have crowd management procedures in place at Tin Hau, Causeway Bay, Wan Chai and Admiralty stations. Trains may also skip stations.