Police said that all 20 people on board the plane, including its three crew members, died.
The Junker plane, which can carry up to 17 passengers and three crew, crashed into the Piz Segnas mountain in the east of the country on Saturday, at an altitude of around 2,500 metres. Most were from Switzerland but also a couple and their son from Austria.
The aircraft was a Junker JU52 HB-HOT plane, built in Germany in 1939 and now a collectors' item.
According to the SwissInfo website, citing local police, the plane went down near the Piz Segnas mountain on the afternoon of August 4 at an altitude of 8,330 feet.
On July 27, four people were killed in a light plane crash at the top of a glacier in the southern Valais canton.
He said hot weather conditions did not contribute to the crash and that the aircraft fell nearly vertically out of the sky at relatively high speed.
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The photo provided by Police Graubuenden shows the wreckage of the old-time propeller plane Ju 52 after it went down went down Saturday Aug, 4 2018 on the Piz Segnas mountain above the Swiss Alpine resort of Flims, striking the mountain's western flank about 2,540 meters (8,330 feet) above sea level.
Swiss police said five copters were involved in the search and rescue operation and the airspace over the crash site was to remain closed until late Sunday.
Although there were eyewitnesses to the crash, the BBC's Imogen Foulkes says that the investigation into what happened will take time.
Officials can essentially rule out a collision with another aircraft or an obstacle such as a wire, Knecht said.
Authorities are investigating what caused the deadly crash. Knecht said that while heat can affect an aircraft's performance, experienced pilots could deal with that.
Each of the pilots flying it had over 30 years of experience in both the military and civilian sector. The airline suspended flights until further notice.