The World Health Organization is launching a $100-million response plan to combat an "unprecedented" outbreak of Ebola in West Africa that has killed 729 people out of 1,323 infected since February, the agency said on Thursday.

WHO Director General Margaret Chan will meet in Conakry, Guinea, on Friday with the presidents of affected West African nations, the United Nations health agency said in a statement.

"The scale of the Ebola outbreak, and the persistent threat it poses, requires WHO and Guinea, Liberia and Sierra Leone to take the response to a new level and this will require increased resources, in-country medical expertise, regional preparedness and co-ordination," said Chan.

The plan identifies the need for "several hundred more personnel" to be deployed in affected countries to ease the strain on overstretched treatment facilities, the WHO said. Clinical doctors and nurses, epidemiologists, and logisticians are urgently needed, it said in an appeal to donor countries

"The plan sets out new needs to respond to the outbreak across the countries and bring up the level of preparedness in neighbouring countries," WHO spokesman Paul Garwood said. "They need better information and infection-control measures."

The plan aims to stop transmission of the virus by strengthening disease surveillance, particularly in border areas, protecting health workers from infection and doing a better job of explaining the disease to communities.

The U.S. Centers for Disease Control and Prevention issued a travel advisory against non-essential travel to Guinea, Liberia and Sierra Leone.

Dr. Thomas Frieden, director of the CDC, said his agency is stepping up its response to the outbreak and will send an additional 50 health experts to assist with efforts to control the outbreak.

Canada's Public Health Agency is not taking that step just yet, instead recommending travellers practise special precautions, such as getting extra vaccinations. According to its online travel notice, the risk of infection is low for most travellers.

Meanwhile, the health conditions of a U.S. physician and a missionary who contracted Ebola while helping fight an outbreak of the disease that has claimed more than 700 lives in West Africa have worsened, two relief organizations said on Thursday.

Dr. Kent Brantly and missionary Nancy Writebol are in "stable but grave condition" in Liberia as they battle the deadly virus, according to North Carolina-based Christian relief groups Samaritan's Purse and SIM. Brantly and Writebol were serving in Monrovia, Liberia, as part of a joint team from the two relief organizations.

Public health emergency in Sierra Leone

In Sierra Leone, President Ernest Bai Koroma declared a public health emergency. He vowed to quarantine sick patients at home and have authorities conduct house-to-house searches for others who may have been exposed as the country struggles with families resisting treatment at isolation centres. Some have kept loved ones at home given the high death rates at clinics where Ebola patients are quarantined.

His announcement late Wednesday came as neighbouring Liberia also increased efforts to slow the virulent disease's spread, shutting down schools and ordering most public servants to stay home from work.

"It could be helpful for the government to have powers to isolate and quarantine people and it's certainly better than what's been done so far," said Dr. Heinz Feldmann, chief of virology at U.S. National Institute of Allergy and Infectious Diseases. "Whether it works, we will have to wait and see."

Ebola now has been blamed for 729 deaths in four West African countries this year, and has shown no signs of slowing down, particularly in Liberia and Sierra Leone. It has also reached Nigeria's biggest city Lagos, where authorities said on Friday a man had died of the virus.

On Thursday, the WHO announced 57 new deaths — 27 in Liberia, 20 in Guinea, nine in Sierra Leone and one in Nigeria.

Among the dead was the chief doctor treating Ebola in Sierra Leone, who was to be buried Thursday.

The government said Dr. Sheik Umar Khan's death was "an irreparable loss of this son of the soil." The 39-year-old was a leading doctor on hemorrhagic fevers in a nation with very few medical resources.

In a measure of rising international concern, Britain on Wednesday held a government meeting on Ebola, which it said was a threat it needed to respond to.

But international airlines association IATA said the WHO was not recommending any travel restrictions or border closures owing to the outbreak, and there would be a low risk to other passengers if an Ebola patient flew.

The outbreak of the hemorrhagic fever, for which there is no known cure, began in the forests of remote eastern Guinea in February, but Sierra Leone now has the highest number of cases.

Sierra Leone's Koroma said he would meet with the leaders of Liberia and Guinea in Conakry on Friday to discuss the epidemic and that he was cancelling a visit to Washington for a U.S.-Africa summit next week.

U.S. Peace Corps withdraw

"Sierra Leone is in a great fight.… Failure is not an option," Koroma said in a speech late on Wednesday, adding that the state of emergency would initially last between 60 and 90 days. "Extraordinary challenges require extraordinary measures."

Medical personnel work at the Doctors Without Borders facility in Kailahun, Sierra Leone, where Dr. Sheik Umar Khan died. (Youssouf Bah/Associated Press) Ebola's symptoms include external bleeding, massive internal bleeding, vomiting and diarrhea in its final stages. The disease kills up to 90 per cent of those infected, though the fatality rate in the current epidemic is running at around 60 per cent.

The president said police and the military would enforce a quarantine on all epicentres of the disease, and would provide support to health officers and NGOs to do their work unhindered, following a number of attacks on health workers by local communities.

House-to-house searches would be implemented to trace Ebola victims and homes where the disease was identified would be quarantined until cleared by medical teams, he said, announcing a ban on all public meetings except those related to Ebola.

Liberia on Wednesday announced the closure of all schools across the country and said it was considering quarantining affected communities.

The U.S. Peace Corps said it was withdrawing 340 volunteers from Liberia, Sierra Leone and Guinea after two of them came in contact with a person who later died of the virus.

New airport controls

Sierra Leone, a former British colony, said passengers arriving and departing Lungi International Airport would be subject to new protocols, including body temperature scans.

Two regional airlines, Nigeria's Arik and Togo's Asky, have cancelled all flights to Freetown and Monrovia after a U.S. citizen died in Nigeria after contracting the disease in Liberia.

Nigeria's civil aviation authority (NCAA) said on Thursday it had started temperature screening passengers arriving from places at risk from Ebola and had suspended pan-African airline Asky for bringing the first case to Lagos.

Patrick Sawyer, the first recorded case of Ebola in Nigeria, took an Asky flight that stopped in Ghana and Togo, raising questions over how a person whose sister had died of the disease three weeks before was able to board an international flight.

Ghana also said it was immediately introducing body temperature screening of all travellers from West African countries at Accra airport and other major entry points, with isolation centres being set up in three towns.

Kyei Faried, deputy director in charge of disease control, told a news conference that authorities had a list of 11 passengers who disembarked from Sawyer's flight and were monitoring them. The government is considering whether to ban flights from affected countries.