The Democratic Republic of Congo has declared a yellow fever epidemic in three provinces, including the capital Kinshasa, after confirming 67 cases of the disease, with another 1000 suspected cases being monitored.
Health Minister Felix Kabange said only seven of the proven cases were indigenous to the central African country, while 58 were imported from Angola, where the outbreak began.
A further two cases came from remote forested areas not linked to the current outbreak. Five people in total have died, Kabange added.
"I declare today a localised epidemic of yellow fever in the provinces of Kinshasa, Kongo Central and Kwango," Kabange told a news conference.
Kinshasa is the primary concern for global health officials since it has a densely-packed population of more than 12 million and poor healthcare infrastructure.
Yellow fever is transmitted by the same mosquitoes that spread the Zika and dengue viruses, although it is a much more serious disease. The "yellow" in the name refers to the jaundice that affects some infected patients.
The global stockpile of vaccines has already been depleted twice this year to immunise people in Angola, Uganda and Congo.
It stands at 6 million doses, but this may not be enough if there are simultaneous outbreaks in multiple highly-populated areas, experts warn.
Almost 18 million doses have been distributed for emergency vaccination campaigns so far in the three African countries.
The current method for making vaccines, using chicken eggs, takes a year.