An outbreak of plague in northeastern Democratic Republic of Congo has killed 61 diamond miners and infected hundreds more, the World Health Organization (WHO) said Friday.

Many of the 7,000 miners working in Zobia, north of the city of Kisangani, have fled since the outbreak began two months ago, and could have spread the highly contagious disease, the United Nations agency said.

“The epidemiological data is still incomplete but we are sure there are at least 61 deaths.

The main problem is that due to panic, maybe two-thirds of the population, ran away from the mine,” Eric Bertherat, head of the WHO team, told reporters.

“There is a risk that some patients in incubation run away and maybe arrive in Kisangani. So it is very important to inform health care workers to alert them of the risk of admission of highly-contagious patients,” he said.

Kisangani is Congo’s third biggest city and a major trading center on the Congo River.

Plague, which is spread between rodents by fleas, can also be transmitted to people through infected rodent flea bites. It has a case-fatality rate of 50 percent to 60 percent among humans if not treated with antibiotics, WHO says.

There are three main forms of plague in humans and the one suspected in the former Zaire is pneumonic plague, which affects victims’ lungs, WHO said.

“It is very important to quarantine, isolate these people who are sick with pneumonic plague so that the transmission is brought under control. If we can find the cases and treat them effectively, this can be stopped,” said May Chu, a WHO expert.

A 10-member WHO emergency team was leaving at the weekend with supplies of antibiotics to try to stem the outbreak and ensure that health workers in the region isolate suspect cases.

But the remote mine in mineral-rich Ituri, reportedly controlled by rebels, is difficult to reach and the team will require U.N. security clearances, officials said.

Cases are still occurring in the mine, where conditions are crowded and unsanitary, and 20 workers were admitted to health facilities in Zobia with symptoms Wednesday, he added.

The diagnosis of plague had been verified through testing, WHO spokesman Dick Thompson said.