GRAND CANYON NATIONAL PARK, Ariz. (AP) — Three hikers died from apparent heat-related illnesses in the Grand Canyon on two separate days in the past week in the inner canyon, where temperatures can exceed 109 degrees Fahrenheit (43 degrees Celsius) in the shade during midday hours, federal officials said Friday.

A 72-year-old man became ill from the heat on June 12 while hiking the South Kaibab Trail and died before rescue crews could reach him. Four days later, a 67-year-old man and a 68-year-old woman also appeared to suffer from heat-related illnesses while hiking the North Kaibab Trail and died before help arrived, the U.S. National Park Service said in a statement.

Despite a rapid response and aerial support, all three hikers were dead by the time first responders reached them, the park service said.

The Grand Canyon has seen an uptick in heat-related illnesses in recent weeks and urged inner canyon hikers to stay off trails between 10 a.m. and 4 p.m., park officials said.

The bodies were taken to the Coconino County Medical Examiner office and investigations of the deaths are ongoing, the National Park Service said.