Authorities in Japan’s ancient capital Nara are warning visitors not to feed the city’s wild deer – a major tourist attraction – after several of the animals died after swallowing plastic bags.

Large amounts of plastic waste were found in the stomachs of nine of 14 deer to have died since March, according to a local wildlife conservation group.

The bags and wrappers are thought to have been discarded by visitors who fed the animals, ignoring signs in English and Chinese warning them to give the animals only approved senbei crackers that are sold in local shops and do not come in plastic packaging.

Officials from the Nara Deer Preservation Foundation discovered masses of bags and other plastic items inside the dead animals’ stomachs, according to Kyodo news agency. One of the deer had swallowed 4.3kg of plastic, it added.

The deer are attracted by the smell of food coming from plastic bags discarded by tourists, who flock to Nara to view its shrines and temples and interact with the estimated 1,300 free-roaming deer in the city’s main park.

Rie Maruko, a vet and member of the conservation group, said the deer died from starvation after plastic and other foreign objects damaged their complex digestive system.

“The deer that died were very skinny and I was able to feel their bones,” Maruko told Kyodo. “Please don’t feed them anything other than the designated senbei snacks.”

Nara’s deer, which have been known to attack visitors who tease them with food or try to take selfies with them, are believed to be divine messengers and were designated natural treasures in 1957.

Local authorities said they would step up requests not to feed the deer unauthorised snacks amid a steep rise in tourism, with the number of international visitors to Nara prefecture rising almost tenfold since 2012 to 2.09 million in 2017.