BERLIN -- Swiss rescue teams held out hope Wednesday that there was still a chance of finding a German billionaire alive even though he has been missing in the Alps for days, but admitted the likelihood of his survival was diminishing rapidly. Karl-Erivan Haub, the 58-year-old heir to the Tengelmann retail empire, was training for a ski mountaineering race when he disappeared on Switzerland's famous Matterhorn peak, located on its southern border with Italy.

Haub was last seen on Saturday morning as he headed up a mountain lift with skis and a daypack, and was reported missing the following morning after he failed to show up at his hotel in Zermatt, said Valais canton (state) police spokesman Mathias Volken.

An immediate search, involving three helicopters, ground patrols and avalanche rescue teams was undertaken on both the Swiss and Italian sides of the border, involving up to about 60 people, said Anjan Truffer, head of the Zermatt rescue station.

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The search was complicated by bad weather -- and had to be temporarily broken off on the Italian side -- and by the fact it was not known specifically where Haub went missing, Truffer said.

"It is a huge area, over 92 sq. miles," Truffer said.

Haub's cellphone was either switched off before or had run out of batteries by the time he was last seen, so rescuers have no signal to track, he added.

Haub was skiing on his own in an area with glaciers and could have fallen into a crevasse, said Bruno Jelk, an experienced mountain rescue expert based in Zermatt.

"The big problem is it's not known specifically where he went missing," Jelk told The Associated Press by phone. "It's a huge area and there are a lot of possibilities. I'd say he must have fallen into a crevasse but there are a lot of them and it's hard to know which one."

He said fresh snow and windy conditions have made it even more difficult for searchers to pick up any traces of Haub's path.

Prosecutors are also involved in the case but spokesman Dominic Lehner said there was no evidence yet to speculate whether "there is a crime or just a tragic accident."

Haub was wearing relatively light training clothes for a one-day outing and had only a daypack but still could be alive if he managed to keep himself warm, said Axel Mann, the head rescue doctor involved in the operation.

"There is a slight chance, and on the rescue side we are all still fully engaged," Mann said.

Tengelmann spokeswoman Sieglinde Schuchardt told the AP that Haub was an experienced skier and mountaineer and that the company was in contact with Swiss authorities.

"Many of us knew Mr. Haub personally. He was an enthusiastic skier ... he came to ski here in Zermatt for at least one or two weeks practically every year," Truffer said.

"As a rule, we always recommend taking a mountain guide," he added. "But given the circumstances -- the conditions were very good, the weather was good and he actually only planned an easy tour -- you can certainly assume that you can justify him being alone. But we still don't know exactly where he wanted to go."

Haub -- who was born in Tacoma, Washington -- and his brother Christian have led Tengelmann since 2000. The family's fortune is estimated at over $3.7 billion. Family patriarch Erivan Haub died in March at his home in Wyoming.

Tengelmann's main businesses are the hardware store Obi and clothing retailer KiK. It also has large stakes in the Netto supermarket chain and online retailer Zalando.