The Ebola outbreak in Congo has spread from the countryside into a city, prompting fears that the disease will be increasingly difficult to control.
Health Minister Oly Ilunga Kalenga confirmed a case in Mbandaka, a city of a million people about 130km (80 miles) from the area where the first cases were confirmed earlier this month.
The city is a major transportation hub with routes to the capital Kinshasa.
Forty-two people have now been infected and 23 people are known to have died.
Ebola is a serious infectious illness that causes internal bleeding and often proves fatal. It can spread rapidly through contact with small amounts of bodily fluid and its early flu-like symptoms are not always obvious.
Senior World Health Organization (WHO) official Peter Salama said the outbreak’s shift to a major city meant there was the potential for an “explosive increase” in cases.
“This is a major development in the outbreak,” he told the BBC. “We have urban Ebola, which is a very different animal from rural Ebola. The potential for an explosive increase in cases is now there.”