Liberia's president has closed all but three land border crossings, restricted public gatherings and quarantined communities heavily affected by the Ebola outbreak in the West African nation.

President Ellen Johnson Sirleaf described the measures late Sunday after the first meeting of a new task force she created and is chairing to contain the disease, which has killed 129 people in the country and more than 670 across the region.

A top Liberian doctor working at Liberia's largest hospital died on Saturday, and two American aid workers have fallen ill, underscoring the dangers facing those charged with bringing the outbreak — the largest in history and the first in West Africa — under control.

Last week, a Liberian official flew to Nigeria and died of the disease at a Lagos hospital. It prompted a quarantine and subsequent week-long shutdown of the hospital, beginning Monday. Staff are being monitored to ensure the virus has not spread.

"The private hospital was demobilized [evacuated] and the primary source of infection eliminated. The decontamination process in all the affected areas has commenced," Lagos state health commissioner Jide Idris told a news conference.

Authorities are monitoring a total of 59 people who were in contact with the victim, including airport contacts, the Lagos state health ministry said. But the airline he flew in with has yet to provide a passenger-list for the flights he used, it added.

No known cure for Ebola

The fact that the victim, Patrick Sawyer, was able to board an international flight despite being ill raised fears that the disease could spread beyond the three countries already affected — Liberia, Guinea and Sierra Leone.

Medical staff working with Doctors Without Borders prepare to bring food to patients kept in an isolation area at an Ebola treatment centre in Kailahun, Sierra Leone. The Ebola outbreak has killed almost 700 people. (Tommy Trenchard/Reuters)

The World Health Organization said in a statement that Sawyer's flight had stopped in Lome in Togo on its way to Lagos.

"WHO is sending teams to both Nigeria and Togo to do followup work in relation to contact tracing, in particular to contacts he may have had on board the flight," WHO spokesman Paul Garwood said.

There is no known cure for Ebola, which begins with symptoms including fever and sore throat and escalates to vomiting, diarrhea and internal bleeding. The disease spreads through direct contact with blood and other bodily fluids as well as indirect contact with "environments contaminated with such fluids," according to WHO. It can kill up to 90 per cent of those who catch it, although the fatality rate of the current outbreak is about 60 per cent.

"No doubt, the Ebola virus is a national health problem," Sirleaf said. "And as we have also begun to see, it attacks our way of life, with serious economic and social consequences."

3 border crossings still open

Sirleaf said all borders would be closed except for three — one of which crosses into Sierra Leone, one that cross into Guinea and another that crosses into both.

Liberia will keep open Roberts International Airport outside Monrovia and James Spriggs Payne Airport, which is in the city.

The U.S. Centers for Disease Control and Prevention said the closure of borders on account of infectious diseases is "quite uncommon" and generally is only called for in "very serious epidemics."

Speaking on a conference call on Monday, CDC officials said sometimes, neighbouring countries might close their borders "out of fear" of the disease being introduced within their boundaries.

They also said that the sheer size of the outbreak means that the response will be "more of marathon than a sprint," officials said.

The incubation period for those who have been exposed to the disease is 21 days. CDC officials say it will take two full incubation periods without a new case in order to declare the outbreak over.

That means even if there were no more cases after today, officials would still have to wait another 42 days before giving the all-clear.

Liberia's Sirleaf said "preventive and testing centres will be established" at the airports and open border crossings, and that "stringent preventive measures to be announced will be scrupulously adhered to."

Other measures include restricting demonstrations and marches and requiring restaurants and other public venues to screen a five-minute film on Ebola.

Outbreak started in Guinea: experts

Sirleaf also empowered the security forces to commandeer vehicles to aide in the public health response and ordered them to enforce the new regulations.

In Sierra Leone, President Ernest Bai Koroma announced Monday he was heading to the east of the country to visit the country's top Ebola doctor who became infected with the disease last week. Officials have said the doctor, Sheik Humarr Khan, has been responding well to treatment at a centre run by Doctors Without Borders in the town of Kailahun. Khan has been described as a national hero for his work fighting the outbreak.

The WHO said that in the past week, its regional director for Africa, Luis Sambo, had been on a fact-finding mission to Guinea, Liberia and Sierra Leone, which have 1,201 confirmed, suspected and probable cases between them.

Experts believe the outbreak originated in southeast Guinea as far back as January, though the first cases weren't confirmed until March. That country has recorded the most deaths, with 319. Sierra Leone has recorded more of the recent cases, however, and has seen 224 deaths in total.

"[Sambo] observed that the outbreak is beyond each national health sector alone and urged the governments of the affected countries to mobilize and involve all sectors, including civil society and communities, in the response," the WHO said.