The World Health Organisation said on Saturday it was investigating "an outbreak of an unknown illness with a high mortality rate" in the Democratic Republic of the Congo.
"The clinical features in the majority of cases include fever, headache, diarrhoea or colicky abdominal pain, and vomiting," the United Nations agency said in a statement.
The WHO said it was not clear how many people had died or the total number afflicted with the illness, though more than half of cases had involved children under the age of 10.
Experts from the WHO as well as Congo's provincial and national health services were in the field and had taken clinical samples for laboratory testing, the WHO said.
It said the cause of the illness was still unknown.
"The national health authorities have taken a precautionary approach and are implementing measures to improve hygiene, ensure the safety of the water supply, promote safe burial practices and strengthen infection control," it said.
