A half-marathoner and two other runners died during the Detroit marathon, organizers said.
Daniel Langdon, 36, of Laingsburg, collapsed at about 9:02 a.m. on Sunday between the 11- and 12-mile (around 17-19-kilometers) markers, said Rich Harshbarger, vice president of consumer marketing for the Detroit Media Partnership.
Rick Brown, 65, of Marietta, Ohio, collapsed at 9:17 a.m., near where Langdon went down, and 26-year-old Jon Fenlon of Waterford collapsed at about 9:18 a.m., just after finishing the half-marathon in 1:53:37, Harshbarger said.
It was unclear whether Brown and Langdon were participating in the 13.1-mile (21-kilometer) half marathon or the full race.
Harshbarger told the Free Press that there were at least six medical stations on the race course and that emergency personnel were on the scene within seconds.
Every runner must sign a medical release form, and they are encouraged to talk to their doctors before they run the race, Harshbarger said.
"On a day when so many people bring such energy and challenge themselves to do their utmost, this news is very difficult to hear," said Free Press editor and publisher Paul Anger said. "Our deepest sympathies are with the families."
The temperature was about 28 degrees (-2.22 Celsius) when the marathon started and had risen to 41 degrees (5 Celsius) by 10 a.m. Running coach Keith Hanson said he doubted that the weather had anything to do with the deaths.
"The wind never kicked up," Hanson said. "In my mind, the conditions were perfect."
Deaths at marathons are relatively rare. The last death at the Detroit event was in 1994 when a 42-year-old man died of a heart attack after running more than 20 miles (32 kilometres).
More than 19,000 people were registered to participate in the 32nd Detroit Free Press/Flagstar Marathon on Sunday.
Nicholas Stanko, of Haslett, Michigan, took first place in the marathon with a time of 2:20:24.
Sarah Plaxton, of Highland, Michigan, was the top female finisher in the marathon with a time of 2:57:09. AP