There is a "very high" public health risk from Ebola in the Democratic Republic of the Congo, the World Health Organisation has said.
The health agency has raised its earlier assessment after one patient in a major city was confirmed as having the disease.
Although the global risk of an Ebola outbreak remains low, the WHO says the risk to countries neighbouring the Congo is now moderate.
On Thursday, a case was confirmed in Mbandaka – a city of about 1.5 million people.
The city lies about 93 miles from Bikoro, a remote area where the current outbreak was announced last week.
Now the disease has been reported in a highly populated urban area, it is expected to spread more quickly.
The confirmed case in Mbandaka, a large urban centre located on major national and international river, road and domestic air routes increases the risk of spread within the Democratic Republic of the Congo and to neighbouring countries, the WHO said.
WHO deputy director-general for emergency preparedness and response Peter Salama has stressed that the agency is certainly not trying to cause panic in the national or international community.
He added: What we are saying though is that urban Ebola is very different phenomenon to rural Ebola because we know that people in urban areas can have far more contacts so that means that urban Ebola can result in an exponential increase in cases in a way that rural Ebola struggles to do.
Later on Friday, the WHO will be convening an emergency committee of experts to advise on the international response to the outbreak.
At the meeting they will decide whether it constitutes a public health emergency of international concern.
If the outbreak reaches Kinshasa, a crowded city where millions live in unsanitary slums not connected to a sewerage system, the situation will become much more concerning.
The WHO statement said there had been 21 suspected, 20 probable and 3 confirmed cases of Ebola between 4 April and 15 May – a total of 44 cases, including 15 deaths.
Mbandaka had three suspected cases in addition to the confirmed case.
The WHO is sending 7,540 doses of an experimental vaccine to try to stop the outbreak in its tracks, and 4,300 doses have already arrived in Kinshasa. It will be used to protect health workers and rings of contacts around each case.
The vaccine supplies will be enough to vaccinate 50 rings of 150 people, the WHO said.
As of 15 May, 527 contacts had been identified and were being followed up and monitored, it said.
(c) Sky News 2018: ‘Very high’ Ebola risk in Democratic Republic of the Congo, says WHO