Nearly 35,000 runners from 45 countries are signed up for one of the five races — the marathon, half-marathon, and the 10k, 5k and 1k races.
The marathon started at 8:30 a.m. on the Jacques-Cartier bridge.
The course takes runners through Île Ste-Hélène, Île Notre-Dame, and several neighbourhoods in the central and eastern parts of the island before reaching the finish line at La Fontaine Park.
The marathon is part of the Rock 'n' Roll Oasis marathon series. Twenty live concerts by local artists are taking place along the various race routes.
Runners are benefiting from warm temperatures for a late September Saturday : Environment Canada says today's maximum temperature is expected to reach 26 C.
Motorists can expect delays for much of the morning and early afternoon as several roads are blocked off .
For people getting to and from the South Shore, the Jacques-Cartier Bridge is closed until noon.
The Metro’s yellow line is in service today. The line has been shut down on weekends for repairs, which will resume next weekend.
See below for a map of the course and road closures.