A team from world health organisation is to decide whether to declare a public health emergency international concern, which would trigger a large response.
At least 44 people are believed to be infected in the current outbreak and 23 deaths are being investigated.
Cases emerged in the rural areas with one now confirmed in the city of Mbandaka.
The city of about one million people is a transport hub on the Congo River, prompting fears that virus could now spread further, threatening the capital Kinshasa and the surrounding countries.
Ebola is an infectious disease which causes internal bleeding and often proves disastrous, it can spread rapidly through contacts with small amounts of bodily fluids, and its early flu-like symptoms are not always obvious.
In West Africa from 2014 to 2016 it killed more than 11,000 people.
The senior WHO officer Peter Salama said “the spread to Mbandaka meant there was the potential for an explosive increase in cases.
“This is a major development in the outbreak he told BBC, “We have urban Ebola which is very different animal from rural Ebola. The potential for explosive increase in cases is now there”.
Mr. Salama, the WHO’s deputy director general for emergency response, said Mbandaka’s location on the Congo river raised precept of Ebola spreading to Congo- Brazzaville and central Africa republic as well as downstream Kinshasa, has a population of 10 million.
“This puts the all different lens on this outbreak and this gives us increased urgency to move very quickly into Mbandaka to stop this new first sign of transmission,” he said.
The 2014 to 16 West Africa outbreak became particularly deadly when it spread to capital of Guinea, Sierra Leon and Liberia.
What is being done to contain the outbreak?
WHO said that of the 44 Ebola cases reported, three are confirmed, 20 are probable, and 21 are suspected. They were recorded in Congo equator province, Mbandaka is a provincial capital.
Mr. Salama said the isolation and rudimentary management facilities have been set up in Mbandaka.
He said that the disease could have been taken there by the people who attended the funeral of an Ebola victim in Bikoro, the south of Mbandaka before travelling the city,
The vaccine from pharmaceutical firm Merck, is unlicensed but was effective in limited trials during the West Africa outbreak.it needs to be stored at a temperature of between 60 and 80c. Electricity supplies in Congo are unreliable.
WHO said health workers had identified 430 people who may have had contact with disease and were working to trace more than 4000 contacts of Ebola patients who had spread across north-west DR Congo.
Why does Ebola keep returning?
There have been three outbreaks in DR Congo since the 2014 to 16 epidemic, Ebola is thought to be spread over long distances by fruit bats and is often transmitted to humans via contaminated bush meat.
It can also be introduced into human population through contacts with the blood organs or other bodily fluids of infected animals. These can include chimpanzees, gorillas, monkeys, antelope and porcupines.
It is possible to eradicate all the animals who might be a host for Ebola. As long as humans come in contact with them, there is always a possibility that Ebola could return.
All the suspected cases are being treated at isolation hospitals in the Democratic Republic of Congo.
By Semusu Peter