All 20 people overseas a German-made Ju-52 plane were killed when the WWII-era aircraft crashed in the Alps, Swiss authorities said on Sunday.
Police have given few details but have confirmed the crash, saying the aircraft came down on a mountainside about 2,540m (8,333 ft) above sea level.
Among those killed were 17 people from Switzerland and a three-person family from Austria.
Ju-Air, a company which offers observation tours in the retro planes, said on Saturday that one of its aircraft was involved in an accident.
"One can ascertain that the aircraft hit the ground almost vertically at high speed", Daniel Knecht, who heads the aviation division of the Swiss Transportation Safety Investigation Board, said.
Police said all onboard were killed in the crash.More news: Tiger Woods gets one last crack at Firestone for WGC final edition
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The plane that crashed had its last maintenance check in late July, Waldmeier said, at which time no defects had been found.
The company's flight operations were suspended, it said.
JU-Air says it runs a small fleet of four Junker planes, all built in 1939, which are for hire.
This file photograph taken on January 1, 1946, shows the first plane to land at the old Beirut airport, a Junkers 52 operated by Compagnie Generale des Transports, which eventually changed its name to Air Liban.
Earlier on Saturday, a small plane carrying two parents and their two children crashed in the nearby canton of Nidwalden.