Four people have died of Ebola in Sierra Leone, the first confirmed cases in the country following an outbreak in Guinea, the health ministry has said.
They died in the eastern Kailahun district, which borders southern Guinea where the outbreak started in March and has killed more than 145 people.
There is no cure or vaccine for Ebola - one of the world's deadliest viruses.
But people have a better chance of surviving if it is identified early and they get supportive medical care.
Ebola can kill up to 90% of those infected and is passed on through contact with the fluids of infected people or animals, such as urine, sweat and blood.
Dr Amara Jambai, the director of disease prevention and control at Sierra Leone's health ministry, said a health worker was among the four people who had died of Ebola.
The deaths had occurred over the last three to four days, he said.
People who developed a fever should immediately report a medical facility and an emergency medical team has been deployed to the remote area, Dr Jambai said.
Ebola virus disease (EVD)
- Symptoms include high fever, bleeding and central nervous system damage
- Fatality rate can reach 90%
- Incubation period is two to 21 days
- There is no vaccine or cure
- Supportive care such as rehydrating patients who have diarrhoea and vomiting can help recovery
- Fruit bats are considered to be the natural host of the virus
The UN World Health Organization said it has been informed about the Ebola outbreak in Sierra Leone and would help deploy essential supplies.
It said it had received information from the field that there had been six deaths - one of which had been laboratory confirmed as Ebola.
Freetown-based journalist Alpha Kamara told the BBC's Focus on Africa radio programme that many people in Kailahun district were staying indoors for fear of catching the virus.
A local chief in the area told him that there had been 11 suspicious deaths between Thursday and Sunday.
In Guinea, there have been a total of 258 suspect and confirmed cases of Ebola, including 174 deaths - 146 of which have been laboratory-confirmed positive.
In Liberia there have been 12 suspected cases, with nine deaths.