Alarm bells sounded yesterday after the outbreak, previously reported in a remote rural area, notched up its first confirmed case in a northwestern city -- the bustling transport hub Mbandaka.
That amounts to bad news for containing and rolling back the haemorrhagic fever virus, experts warned.
"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 has therefore revised the assessment of public health risk to very high at the national level and high at the regional level," it said. "At the global level the risk is currently low. As further information becomes available, the risk assessment will be reviewed."
Separately, the UN's migration agency said it was helping DRC's health ministry to send disease-tracking experts and medical staff to monitor travellers at 16 border points.
A regional bloc, the East African Community -- five of whose six members have borders with the DRC -- said it was on "high alert" over the outbreak and had put in place measures to screen travellers arriving from that country.
The International Committee of the Red Cross (ICRC) said it had mobilised more than 200 volunteers.
"We are totally ready to respond with more support if necessary," the ICRC's national representative, Christine Cipolla, told a press conference in the eastern city of Goma.
The fresh outbreak, publicly declared on May 8, was first reported in a rural part of Equateur Province in the vast country's northwest.
Ebola is both lethal and highly contagious, which makes it difficult to contain -- especially in urban environments where people are mobile and come into more contact with others.
Lacking an arsenal of drugs to treat the virus, doctors isolate patients and trace people who have been in contact with them. This is a major task even for medical services in rich countries, but the DRC is one of the world's poorest countries.
Four times the size of France, the DRC has been chronically unstable and episodically racked by violence since it gained independence from Belgium in 1960. Hospitals, roads, electricity are all major problems, especially in remote areas.
In Mbandaka, whose population is estimated at up to 1.2 million, the mood among many people changed from insouciance to worry yesterday. Bars, restaurants and public offices set up basins of water and soap dispensers for people to wash their hands, while at the city's airport, health ministry workers were taking travellers' temperatures with pistol thermometers, an AFP reporter saw.
Ebola is notorious for its high fatality rate and extreme symptoms, which can include internal and external bleeding.
The virus has a reservoir in tropical African wildlife, being carried by species of bats, which do not themselves fall ill but can pass the pathogen on to humans who hunt for food.
Among humans, the commonest form of infection is through close contact with the blood, body fluids, secretions or organs of someone who is sick with Ebola or has recently died.
The current outbreak -- the ninth to hit the DRC since Ebola was identified in 1976 -- involves the same strain of the virus that struck three West African countries in 2013-15 and sparked an international panic.
It went on to kill more than 11,300 people, in the deadliest ever Ebola epidemic.
The WHO was fiercely criticised over its handling of the epidemic and has pledged to improve its emergency response.There is no licensed drug to treat or prevent Ebola, although an experimental vaccine arrived in the DRC on Wednesday and has been cleared for use by the Kinshasa government.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)