Plastic bags, bottles and other waste are becoming a serious problem for the bears on Hokkaido's Shiretoko Peninsula, and conservationists warn they could begin approaching humans if they acquire a taste for garbage.

The Shiretoko Peninsula is a World Heritage Site and has one of the densest bear populations in the world, according to the Environment Ministry, which estimates that over 200 wild brown bears live in the area.

According to Shiretoko Nature Foundation, a staffer spotted a cub about 80 cm long carrying a plastic bag in its mouth near a road close to a national park area on May 5.

Masato Yoshida, a 31-year-old guide, saw a cub with a plastic bottle near the area on May 17.

"I felt very sad when I saw it," Yoshida said.

Around the area, bear feces containing plastic bags was found in April. The sparsely populated area is believed to have become a dumping ground for garbage ranging from vegetables and fruits to appliances and old tires.

Conservationists are concerned that the bears might get used to foraging for leftovers from plastic bags and begin approaching people in attempts to obtain food.

"Illegal dumping of leftovers could lead to serious danger," warned Tsuyoshi Ishinazaka, a member of the foundation.

The foundation's website says the Shiretoko Peninsula is home to an estimated 500 wild brown bears who share an area about 70 km long and 20 km wide.

The peninsula was designated as a World Heritage Site by UNESCO and draws about 1.2 million tourists annually.