The Police Service of Northern Ireland (PSNI) said its officers expect more than 5,000 spectators at Thursday’s game.
“Supporters, commuters and shoppers are advised to plan their journey in advance, ensuring they leave sufficient travel time as congestion is likely in the area,” a PSNI spokesperson said.
“A build-up of traffic is to be expected in the Shaftesbury Square, Lisburn Road and Donegall Road areas of south Belfast as well as the M1 and Boucher Road areas both before and after the game.”
The match kicks off at 20:00 GMT.
It is technically a Larne home-game but their Inver Park ground does not meet the Union of European Football Associations (UEFA) standard to host Conference League games.
The PSNI spokesperson added: “We hope that the match is enjoyed by all and would remind those attending to behave in a manner befitting the reputation of their teams.”
St Gallen, from the eastern part of Switzerland, have been part of the Swiss Super League for the past decade.
Like Larne, they have lost all of their matches so far in the UEFA league.