Senior officials from Hong Kong and mainland China are to attend the annual flag-raising on the 22nd anniversary of the handover on July 1, 1997.
Pro-democracy activists have called for a march as they have on every anniversary. This year the march is expected to be larger than usual because of widespread opposition to a government proposal that would allow suspects to be extradited to mainland China to face charges.
It will be the third protest in three weeks against the extradition bill.
The government has already postponed debate on the bill indefinitely, leaving it to die. But protest leaders want the legislation formally withdrawn. They are also calling for Hong Kong leader Carrie Lam to resign.
On Sunday, government supporters held a pro-police rally. Hong Kong police have come under criticism for using tear gas and rubber bullets during a crackdown on a protest that left dozens injured June 12.