Although the main Northern Ireland Centennial parade will begin arriving at the City Hall from Stormont around 2.30pm onwards, the last of the 25,000 participants may not arrive in the city centre until after 5.30pm.
Motorists have been advised that traffic disruption is likely into the evening as hundreds of buses will be leaving the city from various locations.
A message on the SSE website states: “Please note that the N.I. Centenary Parade will be taking place in Belfast on Saturday, causing rolling road closures in and around the city. Please plan your journey in advance and leave additional time for your journey to the Arena.”
Grand Lodge Grand Secretary Rev Mervyn Gibson said: “This will easily be twice the size of the annual Twelfth parade in the city, so we are encouraging people to come early and pick their spot because it will be difficult to get parked.”
The PSNI said it will have a traffic management plan in place but delays and diversions can be expected all day.
Chief Superintendent Darrin Jones, Belfast Area, said: “This is a big event with up to 25,000 people expected to take part. We are also anticipating large numbers of spectators along the route.
“We are asking everyone who is planning on travelling through Belfast on Saturday to plan ahead and leave extra time for their journeys.
“We will have traffic diversions and management in place and would ask all visitors to the city to be patient and follow the instructions of marshals and our officers.”