A confirmed Ebola case in the key Democratic Republic of Congo city of Goma is a "potential game changer" in the epidemic that will be assessed by a WHO emergency response board, the UN has said.
World Health Organisation chief Tedros Adhanom Ghebreyesus and the agency's emergency chief, Mike Ryan, both sounded the alarm after an evangelical preacher fell ill in the eastern urban hub.
"The identification of the case in Goma could potentially be a game-changer," Mr Ghebreyesus told a high-level meeting in Geneva, called to refocus attention on the nearly year-old epidemic.
"We cannot be too careful," Mr Ghebreyesus said.
Goma, which has a population of around one million, is the capital of North Kivu province, the epicentre of what is now the second deadliest recorded Ebola outbreak on record.
More than 1,600 people have died since the disease was first documented in the region last 1 August.
Mr Ghebreyesus confirmed he planned to reconvene WHO's emergency advisory board to assess whether the outbreak should be declared a "public health emergency of international concern," a move that steps up the global response.
The panel has held off making this call on three previous occasions, citing the limited risk of large-scale international spread.
But Mr Ghebreyesus explained that because Goma was a "gateway" to Africa's Great Lakes region and the wider world, the international threat level must be re-assessed.
The Goma patient has been described as a pastor who had been on a trip to another town, Butembo, one of the places hardest hit by the outbreak.
There, he preached at seven churches and regularly touched worshippers, "including the sick," the DRC's health ministry has said.
Mr Ryan told reporters that 60 people who had contact with the preacher had been identified so far.
"We are dealing with the 60 contacts we have now," he said.
"We have found and vaccinated 30, and hopefully we will have (vaccinated) the other 30 in the next 24 hours," Mr Ryan said.
The Geneva meeting was largely focused on mobilising further funds to combat the outbreak.
UN humanitarian chief Mark Lowcock stressed that the donor response was not meeting needs on the ground and an upcoming funding appeal would surpass the €133m the UN asked for in February to cover the ensuing six months.
"We need to be honest with ourselves about the real cost of getting to zero cases," Mr Lowcock said.
British international development secretary, Rory Stewart, pledged another €56m, while chastising donors who have been reluctant to step up.
"What I've noticed going around the world trying to get people in this room to contribute is there are a lot of very intellectual, sophisticated reasons that international donors give on why they don't want to give any more money," Mr Stewart said.
"Yes, it's complex, yes it's very difficult, yes, the root causes (of instability in DRC) are difficult to address, but we are in a very, very fragile situation," he said.
"We are going to need considerably more investment if we are to get down to zero in eastern DRC."
The latest Ebola outbreak in eastern Democratic Republic of Congo has so far killed 1,655 people and 694 have been cured, according to a health ministry bulletin in the last few days.
It said 160,239 people had vaccinated.
The World Health Organisation had initially voiced hope it would be able to contain the highly contagious haemorrhagic fever, thanks in part to the new vaccine.
But efforts to tackle the crisis have been hampered both by militia attacks on treatment centres, in which some staff have been killed, and by the hostility of some local people to the medical teams.
Insecurity in the restive region, including a long-standing presence of various rebel groups in Ituri and North Kivu, has also made it difficult for health workers to access those who might have come into contact with Ebola.