Those exposed will for the first time in Congo receive Ebola vaccinations, the health minister said.
World Health Organization has previously admitted that it was too slow to respond to a deadly Ebola outbreak in West Africa from 2014-2016 that killed more than 11,000 people.
One sample proved positive for Ebola, he said. The number of victims of the disease caused by the Ebola virus, may be much higher - at the moment the Ministry of health is aware of 25 deaths linked to the Ebola outbreak has not yet been confirmed, reports "Interfax". The total includes 20 probable cases and 21 suspected ones.
The WHO said it 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".
Mbandaka, a city of nearly 1.2 million, 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. Mbandaka is an hour's plane ride from Kinshasa or a four-to-seven-day trip by river barge, according to a map issued Thursday by the United Nations.
"The confirmed case in Mbandaka, a large urban center located on major national and global river, road and domestic air routes increases the risk of spread within the Democratic Republic of the Congo and to neighboring countries", the statement said. World Health Organization said it is deploying about 30 more experts to the city.
Ebola is lethal and highly contagious, which makes it hard to contain - especially in urban environments where people are mobile and come into more contact with others.
"This is a major development in the outbreak", said Peter Salama, the WHO's deputy director general of emergency preparedness and response.
There is, however, a logistical challenge as the Canadian vaccine, which is called rVSV-ZEBOV, needs to be stored at minus 80 degrees Celsius and is only available in the capital, Health Minister Oly Ilunga told Reuters.
The 2014-16 West Africa outbreak became particularly deadly when it spread to the capitals of Guinea, Sierra Leone and Liberia. The vaccine is thought to be effective against the Zaire strain of Ebola found in Congo. The other death was a suspected case in Wangata, a suburb of Mbandaka on the Congo River, the ministry said.
Similarly, the European Commission has released around 1.6 million euros (1.9 million dollars) to help tackle an Ebola outbreak in Congo, as well as organising flights to transport emergency staff and equipment to the affected areas. Whilst the strategy is being put in place, the "pillars" of an Ebola intervention are taking effect in order to stem the spread of the disease: early treatment and isolation of people who are sick; tracing and following up contacts; informing people about the disease, how to prevent it and where to seek care; supporting existing healthcare; and temporarily changing cultural behaviour around funerals.