Hundreds of troops were deployed in Sierra Leone and Liberia yesterday under an emergency plan to fight the worst outbreak of Ebola, which has killed more than 800 people in West Africa.

Convoys of army trucks ferried 750 troops plus medical workers to Sierra Leone's far east, where the density of cases is highest.

Officials say troops will travel to isolated communities to implement quarantines. Healthcare workers can come and go freely, and the communities will be kept supplied with food.

Attacks on health workers and threats to burn down isolation wards prompted regional governments to impose tough measures last week, including closure of schools and quarantine.

The World Health Organization plans to launch a $100 million response and is holding urgent talks to increase resources in the region. WHO chief Margaret Chan has warned Ebola is outpacing efforts to contain it, and warned of catastrophic consequences.

Health workers say they are overwhelmed by the number of cases, a scenario exacerbated by the departure of some foreign staff after the infection in Liberia of two US workers from the Samaritan's Purse charity.

One of them, Kent Brantly, was improving after being flown back to the United States for treatment. The second staff member, Nancy Writebol, was expected to arrive back in the US today.

The hemorrhagic virus, which has no known cure, has infected more than 1400 people, straining the capacity of under-funded health systems and aid groups to breaking point in one of the world's poorest regions.

The number of cases is also creeping steadily higher in Guinea, where the outbreak started in February. Nigeria's megacity of Lagos yesterday recorded its second case.

In Liberia, President Ellen Johnson-Sirleaf and ministers have held a crisis meeting on anti-Ebola measures as police contained infected communities in the northern Lofa county.

At least 17 bodies have been abandoned on the streets of the Liberian capital Monrovia in recent days, health officials said.