An Ebola epidemic which has killed dozens of people in Guinea's southern forests has spread to the capital Conakry, health sources said on Thursday, confirming four new cases.
The patients were immediately put in isolation centres to avoid the highly contagious virus getting into the population, the sources told AFP.
Conakry, a vast, sprawling port city on Guinea's Atlantic coast is home to between 1.5 and two million people.
Aid organisations have sent dozens of workers to help the impoverished country combat a haemorrhagic fever outbreak which has claimed at least 63 victims in the rural south, many of whom have been confirmed to have been infected by Ebola.
Ebola had never spread among humans in west Africa before February but five deaths being investigated in Liberia, one in Sierra Leone and others still being tested could bring the total in the epidemic to above 70.
The tropical virus -- described in some health publications as a "molecular shark" -- causes severe fever and muscle pain, weakness, vomiting, diarrhoea and, in severe cases, organ failure and unstoppable bleeding.
Scientists have examined 45 samples from victims of the epidemic, with 19 testing positive for Ebola, according to the International Federation of Red Cross and Red Crescent Societies.
Authorities in Conakry on Sunday identified three cases of haemorrhagic fever -- two of them fatal -- but samples taken from the victims tested negative for Ebola.
Other highly-contagious tropical bugs, including Marburg and Lassa, can lead to similar symptoms and have not been ruled out as contributing factors in the epidemic.
Sierra Leone warned on Tuesday that a 14-year-old buried recently may have been infected in Guinea, while the deaths of four women and a boy in Liberia are being tested for the killer virus.
Guinea has banned inhabitants of the south from eating bats, a common feature of the local diet, as the creatures are considered to be the natural host of the virus.
Transmission of Ebola to humans can come from wild animals, direct contact from another human's blood, faeces or sweat, as well as sexual contact or the unprotected handling of contaminated corpses.
British-based charity Plan International says the people of Guinea's southern forests -- the epicentre of the outbreak -- are terrified after seeing neighbours bleeding severely as they were struck down by the virus.
"On Monday, two more deaths were reported in our area. People are really frightened," Joseph Gbaka Sandounou, a unit manager for Plan in Guinea's south was quoted as saying in a statement on Wednesday.
"They have seen people die in a matter of just two or three days. They are constantly worried who is going to be the next fatality."
Doctors Without Borders, which is known by its French initials "MSF", said the spread of the disease was being exacerbated by people travelling to funerals in which mourners touch the dead person's body.
No treatment or vaccine is available, and the Zaire strain detected in Guinea -- first observed in the Democratic Republic of Congo 38 years ago -- has a 90 percent death rate.
Guinea is one of the world's poorest nations despite vast untapped mineral wealth, with a stagnating economy, youth unemployment at 60 percent and a rank of 178th out of 187 countries on the UN's Human Development Index.
Plan, MSF and other aid organisations are providing treatment and sanitation facilities and relaying public health information, especially to schools, via the media and text messages.