Eight lions and 25 elephants have been killed in "human-wildlife conflict" outside a sanctuary in northern Tanzania since last year, authorities said on Tuesday.

The eight lions were speared to death by villagers after they strayed out of the Ngorongoro Conservation Area, a UNESCO World Heritage Site.

Ngorongoro Conservation Area Authority (NCAA) chief conservator, Freddy Manongi, cited human-wildlife conflict as a major cause of declining numbers of lions and elephants in the area.

"It's so sad that we lost seven lions last year and few days ago one lion was speared to death after feasting on someone's cattle. Elephants were also killed after eating into people's farms," Manongi said.

Manongi said the conflict was mainly fueled by the fact that most of the wildlife corridors were invaded by locals for settlements and farming.

"So, carnivores like lions attack livestock and this in turn leads to retaliation by the humans," the official said.

In the latest case, NCAA rangers found two hides of leopard.

Manongi said their fight against poaching was "on top gear", but a big challenge was that wildlife strays out of the national parks.

"We have also introduced regular patrols around the conservancy with coverage of 8292 square kilometers," he said.

The Ngorongoro Conservation Area is located 150 km west of Arusha city, Tanzania's main gateway to tourist destinations.

It is estimated that about 10,000 elephants are killed every year by poachers in Tanzania, which currently has less than 70,000 elephants.

The number of rhinos in Tanzania has declined to 123 from about 10,000 in the 1970s.