The World Health Organisation (WHO) has declared the Ebola outbreak in Democratic Republic of Congo a public health emergency of international concern.
The move should lead to more international support to help tackle the disease.
The outbreak in the DRC has killed more than 1600 people.
This week, the first case was detected in the city of Goma, home to more than a million people.
Declaring a public health emergency of international concern is one of the most important acts the WHO can take.
It has done so only four times before - including for an Ebola outbreak in West Africa which killed more than 11,000 people.
“The government of #DRC is showing exceptional transparency in sharing information every single day.— World Health Organization (WHO) (@WHO) July 17, 2019
They are doing everything it can. They need the support of the international community.
That includes its financial support.” - @DrTedros
The outbreak, the second largest in history, started in August 2018 and is affecting two provinces in DRC - North Kivu and Ituri.
More than 2500 people have been infected and two-thirds of them have died.
It took 224 days for the number of cases to reach 1000, but just a further 71 days to reach 2000. About 12 new cases are being reported every day.
There is a vaccine, which is 99 percent effective. More than 161,000 people have been given it.
However, not everybody is vaccinated - only those who come into direct contact with an Ebola patient, and people who come into contact with them.
The vaccine was developed during the epidemic in West Africa and has been available throughout the latest outbreak.
Why hasn't the outbreak been brought under control?
Tackling the disease has been complicated by conflict in the region.
Since January, there have been 198 attacks against healthcare workers or Ebola treatment facilities leading to seven deaths and 58 injuries.
Another major problem has been distrust of healthcare workers leading to about a third of deaths being in the community rather than at a specialist Ebola treatment centre.
It means those people are not seeking treatment and risk spreading the disease to neighbours and relatives.
There has also been difficulty tracking the spread of the virus.
A significant number of cases are coming as a surprise as those affected have not come into contact with known Ebola cases.
"We are one year into the outbreak and the situation is not getting any better," said Trish Newport, from the charity MSF.
"It's a complex environment with a long history of violence, of conflict, so there's a lot of mistrust of foreigners from outside the area.
"We have to build ties and connections with the community so they trust us."
Could the disease spread further?
The WHO says the risk to neighbouring countries is "very high".
Uganda has already had some isolated cases including two people - a five-year-old boy and his 50-year-old grandmother - who died from the disease. Rwanda is also at risk.
This week a priest died from Ebola in the city of Goma, which is home to more than a million people, is a major transport hub and sits on the DR Congo-Rwanda border,
The WHO said cases there were a "game-changer", however, there have been no reported cases of the disease spreading in Goma.
The WHO has been clear for months that it has insufficient money to tackle the problem.
It had estimated that it needed $98m to tackle the outbreak between February and July. Yet it faced a shortfall of $54m.