Witnesses said they watched a bear emerge from woods 600m away
Brown bears may have returned to Switzerland, more than 100 years after disappearing from its mountains.
Eyewitnesses report seeing a bear high in the Alps near eastern Switzerland's border with Italy, where there is already an established bear population.
Officials say they are still looking for evidence such as bear droppings, hair or tracks to confirm the sighting.
While conservationists would welcome the bears' return, some Swiss shepherds fear for the safety of their flocks.
The Swiss authorities have been keen to see the return of the bear, hunted to extinction along with wolves and lynxes in the Alps in the 19th Century.
Earlier this year, they began to set aside land in the south-east of the country, in the hope it might offer a corridor for bears to spread from northern Italy.
The testimony from three people in Switzerland's Ofenpass National Park suggested at least one bear has made the passage, park officials said.
Some farmers see the return of bears as a threat to their livestock
The witnesses said they had spotted the creature 600m away through binoculars.
They reported seeing it emerge from woodland into an open meadow, where they watched it for 20 minutes. However, failing light meant they were unable to photograph the bear.
The Worldwide Fund for Nature, based in Switzerland, has said bears should be able to adapt to life there, depending on their reception from the local population.
The BBC's Imogen Foulkes in Geneva says some people fear the brown bear may not be greeted warmly by farmers.
A re-established lynx population in the Bernese Oberland is seen as a threat to sheep and cattle, she says, while a lone wolf which strayed from France into Switzerland a few years ago was mysteriously found dead.
But the reappearance of the brown bear may be welcomed by Switzerland as a whole, our correspondent adds.
The Swiss capital, Bern, is named after a bear - although its medieval founder was inspired by the first animal he killed during a day out hunting.
The last bear in Switzerland was killed in 1904.