A French Civil Defence Chopper Eurocopter EC145 with five people aboard crashed on Sunday near the town of Villard-de-Lans in the Auvergne-Rhones-Alpes region, the Isère department prefecture said in a statement.
According to local media outlets, the incident occurred during a rescue operation to help a cyclist injured in the mountains.
The France Bleu news agency reported, citing an eyewitness at the site, that rescuers retrieved two injured persons, covered in blood from the debris. A third person was allegedly in more serious condition and received a cardiac massage on the spot.
French Health Minister Olivier Veran later took to Twitter to say that some of the rescue workers had sustained heavy injuries.
"Shocked by the crash of a civil security helicopter in Isere. Medical teams have been mobilized to help the rescue workers, some of whom are heavily injured."
Footage, appearing to show plumes of smoke, has emerged online, with one Twitter user explaining that two loud bangs were heard after the aircraft went down.
The reason for the incident is unknown. The rescue operation is underway.