French health officials estimate that the country’s historic June heat wave contributed to more than 5,700 excess deaths, according to preliminary research released Wednesday.

The heat wave, which gripped much of France from June 17 to July 2, coincided with 21,674 deaths from all causes in the affected regions, compared with an estimated 15,910 deaths that would have been expected under normal conditions, according to Public Health France. The agency estimated 5,764 excess deaths, a 36% increase above expected mortality, with more than half occurring between June 25 and June 27.