Ebola-hit nations met for crisis talks on Thursday as the death toll topped 1,500 and the World Health Organization warned that the number of cases could exceed 20,000 before the outbreak is stemmed.
Nigeria announced that the virus had reached its oil-producing hub, dashing hopes that the country had successfully contained it to its biggest city, Lagos.
Hopes were raised meanwhile of a vaccine for the haemorrhagic fever after British medical charity the Wellcome Trust and pharmaceuticals giant GlaxoSmithKline said safety trials on a new drug could begin as soon as next month.
But new figures showed the massive scale of the crisis, which the WHO said could cost the international community at least $490 million (370 million euros) to tackle.
Bruce Aylward, the WHO's head of emergency programmes, said that it could take six to nine months to bring Ebola under control, by which time the number of infections could have passed 20,000.
"That's not saying we expect 20,000, that's not saying we would accept, more importantly, 20,000 cases," he told reporters in Geneva, calling the situation a "global health security issue".
"But we have got to have a system that is robust enough to deal with ... a very bad case scenario."
As of August 26, 1,552 people had been confirmed dead from Ebola in four countries -- Sierra Leone, Liberia, Guinea and Nigeria -- while 3,062 had been infected.
But Aylward warned that the actual caseload could be "two to four times higher than the number of cases you see reported".
Health ministers from member states of the West African regional bloc ECOWAS met on Thursday in the Ghanaian capital Accra to discuss how to strengthen its response to the devastating outbreak.
Ghana's President John Mahama, who is current ECOWAS chairman, complained that security measures taken by other countries to prevent the virus spreading, including travel bans, had unfairly hit member states.
"Currently in the sub-region, Ebola is officially reported in four countries and yet the entire West African sub-region of 15 nations and even Africa as a whole of 54 nations has been stigmatised," he told delegates.
As the meeting began, Nigeria's health minister Onyebuchi Chukwu said a doctor in the southeastern city of Port Harcourt had become the sixth person to die of Ebola and the first outside Lagos.
The medic died on August 22, a day after treating a patient who had contact with the Liberian-American man who first brought the virus to Nigeria and who died in a Lagos hospital on July 25.
The patient, an ECOWAS official, slipped through the net and travelled to Port Harcourt where he saw the doctor in a hotel room after feeling unwell, Chukwu said in Abuja.
News of the death came just a day after Nigerian officials claimed to have contained the spread of the virus.
Port Harcourt, 435 kilometres (270 miles) east of Lagos and the capital of Rivers state, is the centre of Nigeria's oil industry and a base for several international companies, including Anglo-Dutch giant Shell, US firm Chevron and France's Total.
Shell and Total said they were both monitoring the situation closely and keeping staff informed of health advice. Operations have not yet been affected.
Nigeria is Africa's biggest oil producer, churning out roughly two million barrels a day, with crude accounting for more than 90 percent of its foreign exchange earnings.
The director of the US Centers for Disease Control and Prevention, Tom Frieden, said on Wednesday "urgent action" was needed to tackle Ebola and warned the situation would get worse before it got better.
There has been mounting concern about the effect of the most lethal outbreak of the tropical virus in history.
A number of airlines, including Air France and British Airways, have suspended their services to Freetown and Monrovia, leading to complaints that Ebola-hit countries were being increasingly isolated.
The WHO's Aylward said it was "absolutely vital" that airlines resume flights because it was hindering the emergency response. A travel ban was "a self-defeating strategy", he added.
On an Ebola vaccine, researchers said they hoped safety trials on 140 healthy volunteers in Oxford, Gambia and Mali could finish by the end of the year, with scope for GSK to make some 10,000 extra doses.
A number of foreign healthcare workers who contracted Ebola have been given an experimental therapy called ZMapp but stocks are exhausted.
Two US doctors have recovered; a Liberian doctor and a Spanish priest died, while a Liberian doctor and nurse, plus a British nurse, are still in treatment.