ALBERTVILLE (France), Dec 9 — French investigators were today seeking to ascertain the cause of the crash of a mountain rescue helicopter in the Alps that left five dead with only the pilot surviving but badly wounded.

The helicopter, an Airbus EC135 operated by a private firm, crashed yesterday evening around the town of Bonvillard just outside Albertville, one of the main resorts in the French Alps.

The prefect, the top local official, for the Savoy region Pascal Bolot said of the five passengers and pilot on board only the pilot had survived but was badly wounded.

Despite difficult weather conditions with fog at the crash site 1,800 metres above sea level, he was evacuated to hospital. Bolot said it was the pilot himself who had raised the alarm.

He added that an investigation has been opened by the prosecutor for Albertville but did not offer any explanation over how the crash happened.

French Interior Minister Gerald Darmanin is also due at the scene later today. Investigators from France’s Bureau of Enquiry and Analysis (BEA) agency for aviation are also set to arrive.

Two of those killed were members of a special mountain police unit for the Alps —  a captain aged 45 and a brigadier aged 39 — who were taking part in a training exercise, France’s national police force said on its Twitter account.

The other three killed were employees of the private firm that operated the helicopter and also employed the pilot.

"To save lives, they take all the risks,” President Emmanuel Macron said in a tweet, paying tribute to those killed and the pilot "fighting for his life”. — AFP