The annual Fat Bear Week contest has begun in Alaska, just days after one of the contestants was killed by a rival.

The competition, which started a decade ago, allows viewers to select their favourite brown bear after the animals have fattened up by gorging on salmon in preparation for winter.

But the beginning of this year's contest was delayed by one day after a female bear was killed by a male bear on Monday.

The entire incident was captured on film as cameras were already set up in anticipation of the contest, which is livestreamed around the world each year.

Voters can pick between a dozen contestants for the crown of Fat Bear at Alaska’s Katmai National Park.

But a pall was cast over this year's event when one of the competitors, bear 402, was fatally mauled by bear 469 on Monday in the Brooks River for reasons that remain unclear.

"National parks like Katmai protect not only the wonders of nature, but also the harsh realities," Katmai National Park and Preserve said in a statement.

"Each bear seen on the webcams is competing with others to survive."

Every year brown bears from the national park devour dozens of salmon a day along the Brooks River with the intention of bulking up before winter.

Twelve bears are chosen for the Fat Bear Week bracket and fans can vote online to decide the winner.

Among the contestants this year is the 2023 champion, Grazer, who is a mother raising her first cub.

Last year's runner-up, Chunk, has yet to secure the title.