Poachers have slaughtered some 200 elephants in a national park in northern Cameroon, about a third of the population, and the massacre is still going on, according to a wildlife protection group.

The International Fund for Animal Welfare (IFAW) said a gang of Sudanese poachers had killed the free roaming elephants in the Bouba Ndjida National Park in northern Cameroon, near the border with Chad, in an unprecedented attack.

"At least 100 elephant carcasses have been found in the park in the past month and ongoing shooting is making it impossible to conduct a further, detailed assessment of the situation," IFAW said on its website.

"It is understood that more carcasses are expected to be found in unexplored regions of Bouba Ndjida."

The organisation said many orphaned elephant calves had been spotted abandoned following the shootings and concerns were high the babies may soon die of hunger and thirst.

"Their deaths will only compound the impact of the poaching spree on the Cameroons threatened elephant populations," it said.

IFAW official Celine Sissler-Bienvenu said it was common for armed gangs of poachers to cross from Sudan during the dry season to kill elephants for their ivory.

"But this latest massacre is massive and has no comparison to those of the preceding years," she said.

"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," Sissler-Bienvenu added.

IFAW said Britain, France, the European Union and the United States had voiced alarm and called on the Cameroon authorities to take urgent action to stop the killing.

Sissler-Bienvenu said the only answer was to end demand for ivory especially in Asia and to ensure conservation officials in range states were provided with skills and the equipment necessary to counter professional gangs of poachers.

"Since 2009 IFAW has provided anti-poaching assessment, training and support to rangers and conservation officials in central African countries which face severe challenges in the fight to end the bloody and cruel illegal ivory trade," she said.

"What these countries now need is the commitment of the international community to financially support these highly skilled and motivated trainees to be able to meet the task of protecting elephants."