A cholera epidemic has killed more than 500 people in the Democratic Republic of Congo, the World Health Organization said Friday, as it prepared to launch a vaccination campaign in Kinshasa.

The United Nations health agency voiced deep concern over the that has infected some 18,000 people, including 517 who have died, since the beginning of the year.

Cholera is endemic in DR Congo, but usually only affects the east of the country.

This time however, the acute diarrhoeal infection has spread west along the Congo river and has reached Kinshasa for the first time in five years.

The capital has suffered 13 cases and two deaths since August 13, Dominique Legros, head of WHO's division, told reporters in Geneva.

"That's very worrisome because it affects places where there is usually no cases of cholera, no immunity in the population, (and) the health staff is not used to cholera cases," he said, pointing out that in such areas the mortality rate is often very high.

In a bid to stem the epidemic, Legros said WHO was sending support materials and experts to DR Congo and that it had decided Friday to support a large-scale in Kinshasa.

In all, some 300,000 people living in the most risk-prone parts of the capital will receive the two-dose vaccine, getting the first jab between September 22 and 25—and the second two weeks later.

"The objective is to try to contain the outbreak and avoid that we have similar situation like we had five years ago," he said, referring to the last outbreak in Kinshasa in 2011, which over a two-year period infected some 2,200 people and killed 88.

Across the country, that outbreak made 21,750 people ill and left 424 dead.

Cholera is transmitted through contaminated drinking water and causes acute diarrhoea, with children facing a particularly high risk of infection.

There are between 1.4 and 4.3 million cases of the disease worldwide each year, and as many as 142,000 deaths, according to WHO statistics.