The WHO was fiercely criticised over its handling of the 2013 outbreak and has pledged to improve emergency response.
DRC now faces a "very high" risk, the World Health Organization said, after the disease was confirmed in one patient in a major city - raising the assessment from "high" previously.
Mbandaka, a city of nearly 1.2 million people, is in a busy travel corridor in Congo's northwest Equateur province and is upstream from the capital, Kinshasa, a city of about 10 million.
Giving reasons why it was not safe for her compatriots to travel to DRC, the Director of Health services Dr Khumo Seipone said Ebola is a highly contagious and virulent disease that now has no cure.
Media captionSome simple techniques can help prevent spread of Ebola.
Previous reports of the disease had all been in remote areas where Ebola might spread more slowly.
Ilunga said Congo now is entering an urban phase of the outbreak, with higher spread potential. "Urban Ebola can result in an exponential increase in cases in a way that rural Ebola struggles to do". "The potential for an explosive increase in cases is now there".
WHO Regional Director for Africa, Dr Matshidiso Moeti said Ebola spreading into an urban area is concerning and WHO along with its partners is working forward to find the voluntary contacts of confirmed Ebola cases in the Mbandaka region.
It said there has been one new death in Bikoro, where the Ebola outbreak was announced last week and where the first death took place. The virus is initially transmitted to people from wild animals, including bats and monkeys.
Isolation zones have been set up in Mbandaka's main hospital, and in Bikoro, WHO said.
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. The other death was a suspected case in Wangata.
The vaccine, from pharmaceutical firm Merck, is unlicensed but was effective in limited trials during the West Africa outbreak.
With the poor infrastructure and electricity supply in Congo, the only challenge that remains with the vaccine is that it has to store it in a cold temperature.
By Tuesday, 527 contacts had been identified and were being followed up and monitored, it said.
"As more evidence comes in of the separation of cases in space and time, and healthcare workers getting infected, and people attending funerals and then travelling quite big distances - it's got everything we would worry about", he told Reuters.
Why does Ebola keep returning?
The DRC is at its ninth Ebola outbreak since 1976. As long as humans come in contact with them, there is always a possibility that Ebola could return.