Two doctors have died of Ebola in Sierra Leone on the same day, a government and a hospital source said, bringing to 10 the number of doctors killed in by the virus in one of the worst-affected countries.

The worst Ebola outbreak on record has torn through some of West Africa's weakest health systems, killing nearly 350 medical personnel, including 106 in Sierra Leone, which is still rebuilding from years of war in the 1990s.

"We are devastated at this haemorrhaging of our healthcare workers," a senior health ministry official told the Reuters news agency, asking not to be named.

There was no immediate comment from authorities but the sources named the two dead doctors.

It is not clear how the men were infected as they were not working on the frontline in an Ebola clinic.

While addressing parliament earlier on Friday, President Ernest Bai Koroma had called medical personnel fighting Ebola the country's "greatest patriots".

Sierra Leone has pledged to pay the families of all medical staff who die battling Ebola $5,000 in compensation.

The latest figures from the World Health Organisation showed Ebola has killed nearly 6,200 people, mainly in Liberia, Sierra Leone and Guinea, since it was confirmed in the region earlier this year.

In an effort to step up the fight against the disease, more than 175 Nigerian medics arrived in Liberia and Sierra Leone on Friday, the first of 600 volunteers promised by a regional giant which contained its own outbreak earlier this year.

The medics will boost weak local health systems that are also struggling to contain other preventable diseases as Ebola discourages people from going to clinics for fear of contracting the fever.

"This is the African spirit you are showing, this is the Nigerian spirit," Nigeria's ambassador to Liberia, Chigozie Obi-Nnadozie, told 76 Nigerian medics who landed there.

Another 100 volunteers landed in Freetown, Sierra Leone.

Months into the Ebola response, experts say they are still short of medical personnel to staff treatment centres.

UN child agency UNICEF on Friday began a campaign to provide 2.4 million people in Sierra Leone with anti-malarial drugs to ease the strain on the healthcare system and allow Ebola cases to be identified more easily. The two diseases have similar symptoms, including headaches, fever and aching joints.

Liberia's President Ellen Johnson Sirleaf issued an order banning rallies and public meetings ahead of a Senate election scheduled for later this month, saying the move was part of the fight against Ebola.

Amid signs of a slowdown in the epidemic in Guinea - where the virus was first detected in March - neighbouring Guinea-Bissau said it would reopen their shared border by next week.