FREETOWN (AFP) - Sierra Leone prepared Thursday for an unprecedented three-day nationwide lockdown to contain the deadly spread of the Ebola virus in a controversial move which experts claimed could worsen the epidemic.

The population of six million will be confined to their homes from midnight (8am Friday Singapore time) going into Friday as almost 30,000 volunteers go door-to-door uncovering patients and bodies hidden in people's homes.

"Rain or shine, the shutdown exercise is going to go ahead. During the three days... the job is going to get done," said Steven Gaojia, head of the government's emergency operation centre.

The worst-ever outbreak of Ebola has claimed more than 500 lives in Sierra Leone, one of three countries at the epicentre of the epidemic which has so far killed almost 2,500.

"Ose to Ose Ebola Tok" - "house-to-house Ebola talk" in the widely-spoken Krio language - will see more than 7,000 volunteer teams of four visiting the country's 1.5 million homes.

They will hand out bars of soap and information on how to prevent infection, as well as setting up "neighbourhood watch"-style community Ebola surveillance teams.

The government has said the teams will not enter people's homes and are not tasked with collecting patients or bodies, but will call emergency services or burial teams "if by chance the teams happen to bump into such situations".

Extra beds have been set up at schools and hospitals across the country, including 200 around Freetown, with the government projecting a 15 to 20 percent upsurge of cases as new patients are discovered.

The ministry of health has enlisted 14 burial teams across the Western Area, which includes the capital, and a fleet of motorcyclists to bike specimens from dead bodies straight to laboratories.

Community activists and civil society leaders have been recruited to help thousands of police and soldiers enforce the curfew.

Health workers, the emergency services and other security forces will be exempt, along with the media and other professionals deemed key workers, while air passengers have been given special dispensation to get to Freetown's airport.

The president was due to launch the shutdown in a televised address to the nation expected on Thursday evening which he has asked tribal chiefs to repeat across the country.

Experts warned however that coercive measures to stem the epidemic, such as confining people to their homes, could backfire badly and would be extremely hard to implement effectively.

Jean-Herve Bradol, a former director of medical aid group Medecins sans Frontiers (MSF) and an emergency physician with experience of working in Africa, said the goal seemed "highly unrealistic".

"The country doesn't have the capacity to visit every household in just three days," he told AFP.

MSF, known in the English-speaking world as Doctors Without Borders, said health workers would find it extremely difficult to accurately identify cases through door-to-door screening.

It warned that lockdowns and quarantines may end up driving people underground "and jeopardise the trust between people and health providers".

"This leads to the concealment of potential cases and ends up spreading the disease further," it said in a statement.

The shutdown has broadly been welcomed by community leaders and local residents of Freetown, however.

"We shall be praying that the operation will end the scrouge. We support the government," said 60-year-old Samuel Johnson, a father-of-three who recently lost a daughter to Ebola.

News of the lockdown has led to a flurry of last-minute shopping in Freetown with large crowds thronging the streets in search of cooking oil, rice, potatoes and yams.

The rush has led to gridlock in parts of the city's already heavily congested roads.

The epidemic, more deadly than all previous outbreaks put together since Ebola was discovered in the Democratic Republic of Congo in 1976, has killed more than half of those infected.

The virus can fell its victims within days, causing severe fever and muscle pain, weakness, vomiting and diarrhoea - in some cases shutting down organs and causing unstoppable bleeding.

No licenced vaccine or specific treatment regime exists, although experts have stepped up their research in response to the crisis.

The United Nations Security Council was due to hold an emergency session on Thursday to discuss ramping up the global aid response to the crisis.

US President Barack Obama has pledged to send 3,000 military personnel to west Africa to combat the epidemic.

The first French Ebola patient - a female volunteer had contracted the killer virus while on assignment in Liberia - was due to be flown home Thursday, according to MSF.

The World Bank warned on Wednesday that fear of the deadly virus is choking economic activity in the worst-hit countries, with potentially "catastrophic" results.