Dressed in round black hats and bright-red waistcoats, the huddled circle of men burst into song, their falsetto voices echoing across the mountain valley: “Yodelayheehoo”.

High in the Alps, the resort of Davos is playing host to the Swiss Federal Yodelling Festival, a three-yearly magnet for lovers of mountain folk music and the region’s centuries-old traditions.

“You flip between singing from your head and your diaphragm.”

“It’s all in the technique,” said 35-year-old Roger Bider, as bystanders applauded his eight-man group’s spontaneous performance on a station platform.

“You flip between singing from your head and your diaphragm,” said the soft-spoken Bider, one of two yodellers whose fellow singers provided a bass-voice backing.

A group of Swiss Alphorn blowers perform at the festival. Photo: AAP

Known internationally for the annual World Economic Forum gathering of business and political leaders, this is the first time Davos is hosting the four-day yodelling festival.

The national event, which wraps up on Sunday and is broadcast live on Swiss television and radio, first began in 1924 and draws 10,000 traditionally-clad participants and 100,000 fans.

While the events have juries, it’s hardly a battle of the bands: there are no prizes, beyond respect.

But for many attendees, yodelling is about more than just music.

“You get hooked,” explained Paul Mettler, 62, of the Swiss Yodelling Association, which supervises the event.

“There’s also the camaraderie. At events, you meet people you know, and make new friends, too,” said Mettler, who took up yodelling in 1993.