DETROIT (WXYZ) - Waves of runners crossed the starting point for the Detroit Free Press Marathon, beginning at 6:58 a.m. Sunday.
Race officials expected more than 25,000 marathon participants and around 50,000 spectators to take part in the event.
Police stepped up security in wake of the bombings at the Boston Marathon earlier this year, but the Detroit event began without any issues.
The Detroit Free Press Marathon is the only one in the United States that crosses an international border. The route takes runners across the Ambassador Bridge into Canada and underwater through the Detroit-Windsor Tunnel into Canada.
The Detroit Free Press Marathon is a competitive race and requires runners to complete the route by 2 p.m.
Several roads were closed because of the marathon route. For a list of road closures, click here .