The Ebola death toll in Guinea has risen to 80, while 122 suspected cases have been registered, health authorities say.
The outbreak is "unprecedented" because the spread of the disease across the small West African nation makes it very difficult to control, according to the medical charity Medecins Sans Frontieres.
"We are facing an epidemic of a magnitude never before seen in terms of the distribution of cases in the country," said the groups' project co-ordinator, Mariano Lugli on Tuesday.
President Alpha Conde announced a "health emergency" but snubbed Guinea's northern neighbour Senegal, which closed its borders to protect its population from the virus, for "causing panic".
In Liberia, to Guinea's southeast, at least two people have died from the virus. The health ministry announced at least 11 suspected cases last week.
Ebola is one of the most contagious viral diseases known, often resulting in death. The virus cannot be prevented with a vaccine and is untreatable with medication.
