A cross country meet at Lehigh University was stopped after 18 people were taken to the hospital for heat exhaustion, official said.
The Paul Short Race features collegiate and high school runners.
Most of the runners were suffering from dehydration, and emergency crews were overwhelmed by the amount of runners being treated, officials said.
"We along with many other towns in the county have outdoor events going on in the heat today," Lehigh Director of Facilities Greg Schulze on the university's website. "Due to the weather, the emergency services have been overwhelmed and spread thin. It is in the best interest of the athletes to shut down the event."
Four emergency room physicians and six trainers from St. Luke's were on hand, in addition to the Lehigh Sports Medicine staff and county EMS services, according to the Lehigh University website.