At least 77 people, most of them children, have died in northern Angola after an outbreak of a disease the World Health Organization (WHO) suspects to be acute hemorrhagic fever, officials said on Friday.

They have ruled out the Ebola virus - a type of hemorrhagic fever and one of the world’s deadliest diseases - but are urging people to avoid travel to Uige, about 140 miles north of Luanda.

“Most of the city has been affected, but some areas are worse hit than others. We ruled out Ebola on Monday,” Health Ministry spokesman Carlos Alberto said.

Diplomatic sources in Luanda said they understood the airport in Uige had been closed.

Jose Caetano, a WHO spokesman in Angola, said most of the victims were children with symptoms including fever, vomiting and diarrhea. He said at least 77 of the total of 83 people believed infected had died.

“The situation is now under control. Our problem is trying to get the sick to go to health centers. We are trying to encourage people who feel any of the symptoms to get medical attention as quickly as possible,” he told Reuters in Luanda.

Caetano said Angola’s limited laboratory facilities had hampered identification of the disease and that samples had been sent to the U.S. Centers for Disease Control in Atlanta and the Pasteur Institute of Dakar in Senegal.

He said the first case had been detected in November.

Alberto said a specialized medical team was already on the ground in Uige and a national commission had been created to respond to the outbreak.