Fans of polar bear Knut are laying flowers at Berlin zoo to mourn the sudden death of the bear who as a cub became a household name.

The four-year-old bear died suddenly in his enclosure on Saturday afternoon. He waded into the water before having a short spasm and then dying in front of hundreds of zoo visitors.

Rejected by his mother at birth on December 5, 2006, along with his twin brother, who only survived a couple of days, Knut first attracted attention when his main caregiver camped out at the zoo to give the button-eyed cub his bottle every two hours.

Fan clubs soon sprung up across the globe, including in Japan, the United States and Germany.