The WHO is also deploying 30 experts to Mbandaka to "conduct surveillance in the city and is working with the Ministry of Health and partners to engage with communities on prevention and treatment and the reporting of new cases".
Humans can be infected by other humans if they come in contact with body fluids from an infected person or contaminated objects from infected persons.
Health workers are sprayed with chlorine after leaving an isolation ward with suspected Ebola patients at Bikoro Hospital - the epicenter of the latest Ebola outbreak in the Democratic Republic of Congo.
Officials said there are 44 suspected, probable or confirmed cases of Ebola and that 23 people have died have died so far.
The worst-ever Ebola outbreak started in December 2013 in southern Guinea before spreading to neighbouring west African countries Liberia and Sierra Leone, killing more than 11,300 people out of almost 29,000 registered cases.
Ebola, a hemorrhagic disease which is endemic to tropical regions of sub-Saharan Africa, was identified in the 1970s, but historically claimed a relatively small number of lives, despite its mortality rates reaching as high as 50 percent, as its spread between isolated villages and towns was limited. Laboratory tests on two samples from Wangata confirmed one specimen as positive for Ebola, while the other was negative.
"With the new case confirmed in Mbandaka, the scenario has changed, and it has become more serious and worrying, since the disease is now affecting an urban area", said Henry Gray, MSF emergency coordinator in Mbandaka.
Mbandaka, in the Democratic Republic of Congo, has a population of about 1.2 million and is a hub for trade and travel in the absence of a functioning road network in the region.
At present, 514 people who may have been in contact with infected people have been notified by the national health authorities, and they are now under monitoring.
Last week, a top World Health Organization official warned that if the virus reached Mbandaka, the DRC could be confronted with yet another Ebola crisis.
The aid group Medecins Sans Frontieres said 514 people who are thought to have been in contact with infected people were now being monitored.
On Wednesday more than 4,000 doses of an experimental vaccine sent by the World Health Organization arrived in Kinshasa with another batch expected soon.
"This puts a whole different lens on this outbreak and gives us increased urgency to move very quickly into Mbandaka to stop this new first sign of transmission", he said.
He said the disease could have been taken there by people who attended the funeral of an Ebola victim in Bikoro, the south of Mbandaka, before travelling to the city.
The vaccine has been shown to be highly effective against Ebola.
Nine Ebola outbreaks have occurred in DRC since the virus was first identified in 1976.
An outbreak between 2014 and 2016 in west Africa was the worst ever, and killed more than 11,000. Symptoms include fever, vomiting, diarrhea, muscle pain and at times internal and external bleeding.