Three doctors in Liberia with Ebola who started taking an experimental drug last Thursday are showing remarkable signs of improvement, a minister said.
The drug, ZMapp, was first given earlier this month to two US aid workers who were flown home for treatment from Liberia, according to the BBC.
Ebola has no cure but the World Health Organization (WHO) ruled that untested drugs can be used in light of the scale of the outbreak in West Africa.
ZMapp is produced by North American companies, in conjunction with US and Canadian government agencies.
The virus in West Africa has killed 84 more people in just three days, bringing the total death toll to 1229.
The outbreak began in Guinea and is devastating communities in Liberia, Sierra Leone, and has a toehold in Nigeria, Africa's biggest economy.
Liberia has imposed a night-time curfew and has quarantined a slum in the capital Monrovia in a bid to halt the spread of the virus.
The WHO had also expressed "cautious optimism" the spread in Nigeria can be stopped.
Ebola is transmitted by direct contact with the body fluids of an infected person.
Initial flu-like symptoms can lead to external haemorrhaging from areas such as eyes and gums, and internal bleeding which can cause organ failure.
Public health officials in New Zealand have been given extra powers to hold planes and ships at the border if there is concern that a person on board is infected with the deadly virus.
However, Associate Health Minister Jo Goodhew said the risk of Ebola reaching New Zealand was extremely low.
Two New Zealand nurses, Donna Collins and Sharon Mackie, have travelled to West Africa for three weeks to join the international Red Cross team responding to the outbreak.