Poachers have slaughtered at least 200 elephants in the past five weeks in a patch of Africa where they are more endangered than anywhere else on Earth, wildlife activists say.

The money made from selling elephant tusks is fuelling misery throughout the continent, the International Fund for Animal Welfare warned.

Many elephant calves orphaned by the recent killings have been spotted in Cameroon's Bouba Ndjida National Park and activists fear the animals may soon die of hunger and thirst.

"Their deaths will only compound the impact of the poaching spree on the Cameroon's threatened elephant populations," the organisation said.

It is not known how many elephants remain in the West African nation. The latest figures from the International Union for Conservation of Nature estimated there were only 1,000 to 5,000 left in 2007.

The fund blamed poachers from Sudan, who it said were crossing through Chad to reach the remote northern Cameroonian wildlife reserve. Ongoing shooting is making it impossible to conduct a detailed assessment, activists said.

The fund said armed insurgents had crossed porous borders on poaching raids for years, but it called the scale of this year's killings "massive and unprecedented."

Embassies of the United States, the European Union, Britain and France had sounded alarm bells about the slaughter and had called on Cameroon's government to take urgent action to stop the killing.

"The ivory is smuggled out of West and Central Africa for markets in Asia and Europe, and the money it raises funds arms purchases for use in regional conflicts, particularly ongoing unrest in Sudan and in the Central African Republic," said the fund's Paris-based spokeswoman Celine Sissler-Bienvenu.

Wildlife experts said recently that large seizures of elephant tusks made 2011 the worst on record for elephants since ivory sales were banned in 1989. The fund said estimates suggested as many as 3,000 elephants were killed by poachers across the continent last year.