GRAND BORNAND, FRANCE, JULY 15 -- A "tidal wave" of mud demolished an Alpine campground here yesterday and authorities searched today for bodies in the wreckage of inundated cars and vans. By nightfall, they had recovered 20 bodies, while 28 persons were missing.

The slide, on Bastille Day, was caused by heavy rains that struck as hundreds of people were enjoying the end of a long holiday weekend. The Borne, a mountain stream, became a raging torrent. Debris that had built up above the popular Alpine valley campground in southeastern France swept down on tents and trailers without warning.

"We've never seen such a thing," said Grand Bornand Mayor Pierre Pochat. Normally in summer, "you can cross this stream without wetting your feet."

A temporary morgue was set up in a church, and authorities recovered bodies carried as far as 25 miles downstream. Up to 500 rescue workers searched along the muddy river banks and conducted house-to-house inquiries in the village of Grand Bornand for people on the register at the campsite.

Daniel Philippe, an aide to Jean Jouandet, the local governor, put the death toll at 20, saying 15 bodies were found in France and another five in the Arve River on the outskirts of Geneva, Switzerland, about 25 miles away.

Ten of the dead had been identified, and all were French, Jouandet said. Up to 28 others were missing, he said. At least nine people were seriously hurt, and dozens were treated for shock.

Witnesses, residents and police said a barricade of mud and debris that apparently accumulated in the Borne during the storm broke, washing over the campground at about 6:40 p.m. yesterday. About 150 campers and 70 trailers were at the site.

Peter Massman, 39, of Abingdon, England, told the London Evening Standard that he, his wife, Rosalyn, and children Jan, 9, and Olivia, 6, were in their trailer when a heavy rain started about 5:30 p.m.

"As I looked out of the window from our caravan, I noticed that the river was rising and it contained a lot of debris," he said.

"I said to my wife we must get the children out," Massman said. "We got into our car and drove to the other side of the camping ground where we were able to park our car on a higher level. As we got out of the car, I saw a tidal wave, a sea of mud coming towards us. The whole place was going up."

The Massmans said they climbed the bank to about 50 feet above the campsite and watched as their trailer was swept down the river.

"I lost my wife and my 17-year-old daughter," said a man who identified himself only as Mr. Nivelle. "I'll never get them back. They were taken away with the camper."

@Villagers of Grand Bornand visit campground deluged by flooded River Borne.