Patrick Ivuti, right, of Kenya, crosses the finish line ahead of Jaouad Gharib, left, of Morocco, 07 Oct 2007

Hundreds of runners at a marathon in Chicago needed medical help during a race Sunday in unseasonable heat and high humidity.

Organizers stopped the event after 3.5 hours because of the humidity and temperatures reaching above 31 degrees Celsius.

Organizers said they feared emergency personnel would have been overwhelmed with all the people who may have needed medical care.

A 35-year-old Michigan police officer collapsed and died during the race, but an autopsy showed his death was due to a heart condition, and not heat-related.

More than 300 runners needed medical attention, including some who were hospitalized. Television footage showed medical personnel treating exhausted runners who collapsed along the roadway.

Some participants said organizers did not provide enough water on the course of the 42-kilometer run.

In Arlington, Virginia, a participant in an Army 16-kilometer race collapsed and died near the finish line of the event Sunday.

In Chicago, Kenyan runner Patrick Ivuti won the marathon in 2:11:11. Berhane Adere of Ethiopia defended her title as female champion with a win in 2:33:49.