The World Health Organization (WHO) has warned that Ebola is now entrenched in the capital cities of all three worst-affected countries and is accelerating in almost all settings.
WHO deputy head Bruce Aylward warned that the world's response was not keeping up with the disease in Guinea, Liberia and Sierra Leone.
The three countries have appealed for more aid to help fight the disease.
The outbreak has killed more than 3,860 people, mainly in West Africa.
More than 200 health workers are among the victims.
Speaking on Thursday, Mr Aylward said the situation was worse than it was 12 days ago.
"The disease is entrenched in the capitals, 70% of the people affected are definitely dying from this disease, and it is accelerating in almost all of the settings," he said.
The medical charity Medecins Sans Frontieres (MSF) reported a sharp increase of Ebola cases in the Guinean capital, Conakry, dashing hopes that that the disease was being stabilised there.
Speaking to the BBC on Friday, MSF President Joanna Liu called for urgent international action.
"We're not winning the battle," she said.
"To get ahead of the game we're going to need to deploy much more massively than what we have done so far."
At least one in 20 of those killed in the latest outbreak were medical workers, she said.
Meanwhile in Spain, seven more people are being monitored in hospital for Ebola.
They include two hairdressers who came into contact with Teresa Romero, a Madrid nurse who looked after an Ebola patient who had been repatriated from West Africa.
Ms Romero is now very ill and reported to be at serious risk of dying.
- More than 1300 Nigerian peacekeeping troops have been quarantined in Liberia after coming into contact with a Sudanese man who later died of the disease
- In Liberia, senate elections due next week have been postponed to help reduce the risk of voters spreading the virus
- More details of how passengers at some British airports will be screened are expected to be announced later on Friday
- The US begins its programme of enhanced screening this weekend at five of its major airports, including JFK
- A Texas county sheriff deputy quarantined after visiting the home of the first person diagnosed with Ebola in the US has been given the all-clear.
- Avoid direct contact with sick patients
- Wear goggles to protect eyes
- Clothing and clinical waste should be incinerated and any medical equipment that needs to be kept should be decontaminated
- People who recover from Ebola should abstain from sex or use condoms for three months
'Our people dying'
On Thursday top US medical official Thomas Frieden said that the Ebola outbreak in West Africa was unlike anything since the emergence of HIV/Aids.
He told a meeting in Washington: "In the 30 years I've been working in public health, the only thing like this has been Aids," he said.
Sierra Leone President Ernest Bai Koroma told the meeting that "our people are dying".
He said that the world was not responding fast enough as children were being orphaned.
A Liberian doctor died of the disease at a treatment centre in Monrovia on Thursday.
His death brings to four the number of doctors who have died in Liberia since the outbreak.
The EU has announced plans for a system to evacuate international staff from Ebola-infected countries if they show signs of the disease.
The move is expected to make it easier to deploy European medical workers to combat the crisis in West Africa.
Nigeria's government says 200 healthcare workers have volunteered to be sent to Liberia, Sierra Leone and Guinea as part of a global response team on Ebola.
Nigeria, which has had seven confirmed deaths from the virus, seems to have successfully contained the spread of the haemorrhagic fever, the BBC's Chris Ewokor in Abuja says.
Protective Ebola suit×
The cap forms part of a protective hood covering the head and neck. It offers medical workers an added layer of protection, ensuring that they cannot touch any part of their face whilst in the treatment centre.
Goggles, or eye visors, are used to provide cover to the eyes, protecting them from splashes. The goggles are sprayed with an anti-fogging solution before being worn. On October 21, the US Centers for Disease Control and Prevention (CDC) announced stringent new guidelines for healthcare personnel who may be dealing with Ebola patients. In the new guidelines, health workers are advised to use a single use disposable full face shield as goggles may not provide complete skin coverage.
Covers the mouth to protect from sprays of blood or body fluids from patients. When wearing a respirator, the medical worker must tear this outer mask to allow the respirator through.
A respirator is worn to protect the wearer from a patient's coughs. According to guidelines from the medical charity Medecins Sans Frontieres (MSF), the respirator should be put on second, right after donning the overalls.
A surgical scrub suit, durable hospital clothing that absorbs liquid and is easily cleaned, is worn as a baselayer underneath the overalls. It is normally tucked into rubber boots to ensure no skin is exposed.
The overalls are placed on top of the scrubs. These suits are similar to hazardous material (hazmat) suits worn in toxic environments. The team member supervising the process should check that the equipment is not damaged.
A minimum two sets of gloves are required, covering the suit cuff. When putting on the gloves, care must be taken to ensure that no skin is exposed and that they are worn in such a way that any fluid on the sleeve will run off the suit and glove. Medical workers must change gloves between patients, performing thorough hand hygiene before donning a new pair. Heavy duty gloves are used whenever workers need to handle infectious waste.
A waterproof apron is placed on top of the overalls as a final layer of protective clothing.
Ebola health workers typically wear rubber boots, with the scrubs tucked into the footwear. If boots are unavailable, workers must wear closed, puncture and fluid-resistant shoes.