The BBC's Caroline Wyatt: "Calls are being made for more checks on the sport"

Police are still searching for two more people, but are not hopeful of finding them alive.

The victims were part of a group of 45 tourists and eight guides hit by a sudden flood in the Saxeten Bach Gorge near the resort of Interlaken.

The police and local authorities in Interlaken have said it is still too early to say who was responsible for the accident.

However, an investigation has already begun into whether the Swiss holiday company Adventure World, based in nearby Wilderswil, was negligent in sending out a party just as a storm was brewing.

The group had been canyoning - an adventure sport which involves climbing down gorges and body surfing down mountain rapids and waterfalls without a raft.

A local police spokesman said the victims came from Australia, New Zealand, the UK, Canada, the United States, South Africa and Switzerland. Six more people are injured.

Post mortem examinations are now being carried out.

The police said it would take "days or weeks" until all the victims were identified.

Most of the dead suffered severe head injuries and they were all wearing identical protective gear - so dental records will have to be used for identification.

Flowers were left outside the holiday company HQ

The survivors are being cared for locally as the police continue their hunt for the missing.

Police said they would keep on searching until dark and would resume on Thursday.

The Swiss Government sent its condolences to the victims of nature's "wild behaviour".

Sports Minister Adolf Ogi said: "Our country and the world have lost the hopes, the dreams, the unfulfilled potential of these men and women. We are all the poorer for it."

Flash flood

Georg Hoedle, one of the company's managers, said: "Something absolutely extraordinary, incomprehensible and unforeseeable must have happened, because our guides know every centimetre of the river."

The BBC's Caroline Wyatt in Interlaken says eye witnesses reported that the waters of the Saxeten brook rose rapidly as the storm gathered force.

A flash flood suddenly occurred, bringing down a hail of rocks from the sides of the creek. The waters rose several metres above their usual level, leaving most of the canyoners with little hope of escaping up the steep sides of the gorge.

The stream flows into a river which in turn empties into Lake Brienz around 60km (37 miles) southeast of the Swiss capital, Bern.

The accident was discovered at around 1800 local time on Tuesday (1600 GMT) by a jogger who saw bodies floating into Lake Brienz.

Adrenaline rush

The Swiss authorities have said they would now be examining whether tighter limits should be imposed on sports such as canyoning.

Canyoning is considered dangerous even in good weather conditions

Government official Samuel Bhend said: "There are questions about these adventure holidays and how far we should go in search of an adrenaline rush.

"Maybe we should learn again to respect the limits set by nature."

Tuesday's tragedy was by far the worst canyoning accident to happen in Switzerland, although at least three people have died since 1994 while pursuing the sport there.