Philadelphia (CNN) -- Two runners died while participating in Sunday's Philadelphia Marathon, the race's director said.
Melanie Johnson, executive director of the Philadelphia Marathon Race Weekend, said in a statement that race organizers "are deeply saddened" by the deaths.
The two runners' identities were not immediately disclosed, as officials were still working to notify their families, according to Johnson. That information will be provided to the public "as it becomes available," she added.
"Our thoughts remain with the runners' families and friends," Johnson said.
The marathon runs throughout Philadelphia, with much of the course set along the Schuylkill River. Runners go past historic sites including Betsy Ross's house and the Liberty Bell, in and out of Fairmount Park, and through districts such as Manayunk and University City.
Unlike some other marathons, the Philadelphia Marathon "is open to all competitors" as participants do not have to have a qualifying time to enter, according to the race's website. But officially, all must register in advance to participate.
Cool temperatures, light winds and mostly cloudy skies were the rule during the race, which began at 7 a.m.
"It was perfect running weather, ideal for any runner. You would expect it more if there was really high humidity and hot conditions," runner Jamie DiMeglio told CNN affiliate WPIV, expressing shock at the two runners' deaths.
Folisho Tuko, a resident of High Falls, New York, who is of Ethiopian descent, won Sunday's men's race with a time of 2 hours, 19 minutes, 14 seconds. The women's title went to Mariska Kramer, with the Dutch woman running in a time of 2 hours, 35 minutes, 46 seconds to win for the second straight year.