Image copyright EPA Image caption President Sirleaf said that extraordinary measures were necessary for the survival of the people of Liberia

Liberian President Ellen Johnson Sirleaf has declared a state of emergency as the country grapples with an outbreak of the deadly Ebola virus.

Speaking on national television, she said some civil liberties might have to be suspended.

The Ebola outbreak has also hit Guinea, Sierra Leone and Nigeria, killing more than 930 people.

World Health Organization (WHO) experts are meeting in Geneva, Switzerland, to discuss a response to the outbreak.

The two-day meeting is expected decide whether to declare a global health emergency.

Ebola, a viral haemorrhagic fever, is one of the deadliest diseases known to humans, with a fatality rate in this outbreak of between 50% and 60%. It is spread through contact with the bodily fluids of Ebola patients showing symptoms.

Analysis: Jonathan Paye-Layleh, BBC News, Monrovia

Image copyright EPA Image caption Most of the latest Ebola fatalities have come from Liberia

Already reports are reaching Monrovia that a military blockade is stopping people from western regions of Grand Cape Mount and Bomi, where Ebola is prevalent, from entering the capital.

These counties largely rely on Monrovia for their goods - and the blockade means that the cities of Robertsport and Tubmanburg are now cut off. One Tubmanburg resident phoned into a radio show to complain that rice, the national staple, was already in short supply in the market.

The head of the National Health Workers Association said while the state of emergency was necessary, people should have been given time to prepare. Fear has prompted hospital workers to abandon clinics - meaning many are now shut.

President Sirleaf said this meant many diseases prevalent during the rainy season, such as malaria and typhoid, are going untreated and may lead to unnecessary and preventable deaths.

A WHO statement on Wednesday said 932 patients had died of the disease in West Africa so far, mostly in Liberia, where 282 have died.

Announcing a 90-day state of emergency, President Sirleaf said the government and people of Liberia required "extraordinary measures for the very survival of our state and for the protection of the lives of our people".

Image copyright EPA Image caption The Liberian president said that ignorance and poverty, as well as entrenched religious and cultural practices, were exacerbating the spread of Ebola in her country

Image copyright EPA Image caption Nurses in Liberia have been briefing the public about the spread of Ebola

Image copyright AP Image caption Health experts say that clearly delivered public information is of paramount importance in fighting the disease

She said "ignorance and poverty, as well as entrenched religious and cultural practices, continue to exacerbate the spread of the disease".

Observers say the Ebola crisis in Liberia has got worse because many people are keeping sick relatives at home instead of taking them to isolation centres.

Media playback is unsupported on your device Media caption Tarik Jasarevic, from the WHO, said there were safety and ethical issues surrounding experimental Ebola drugs

Amid international concern, US President Barack Obama said the illness "can be controlled and contained very effectively if we use the right protocols".

"The countries affected are the first to admit that what's happened here is the public health systems have been overwhelmed. They weren't able to identify and then isolate cases quickly enough.

"As a consequence, it spread more rapidly than has been typical," he added.

Mr Obama said that the US was working with Europe and the WHO to provide resources to contain the epidemic.

In other developments:

A Spanish priest who contracted Ebola while working in a hospital in Liberia has been flown back to Spain for treatment, along with a nun who is to be isolated in case of infection

Security forces in Sierra Leone have now imposed a complete blockade of Kenema and Kailahun districts in eastern Sierra Leone - only allowing access for essential services

Saudi Arabian authorities said that a Saudi man who was treated for Ebola-like symptoms after visiting Sierra Leone has died at a hospital in Jeddah. If confirmed, it would be the first Ebola-related death outside Africa

Two US aid workers who contracted Ebola in Liberia appear to be improving after receiving an unapproved medicine ahead of their evacuation back to the US

Concern has also been growing over a number of new cases in Nigeria, the region's most populous nation. On Wednesday, a nurse who treated an Ebola patient became the second person to die of the disease there.

Nigeria's Health Minister Onyebuchi Chukwu described the outbreak as a national emergency, adding that "everyone in the world is at risk" because of air travel.

In a surprise move, the WHO said on Wednesday it would convene a meeting of medical ethics specialists next week to decide whether to approve experimental treatment for Ebola.

Some leading infectious disease experts have been calling for experimental treatments to be offered more widely to treat the disease.

The aim of the WHO's emergency committee meeting is to focus solely on how to respond to the Ebola outbreak.

If a public health emergency is declared, it could involve detailed plans to identify, isolate and treat cases, as well as impose travel restrictions on affected areas.

There is no cure or vaccine for Ebola - but patients have a better chance of survival if they receive early treatment.

Ebola has initial flu-like symptoms that can lead to external haemorrhaging from areas like eyes and gums, and internal bleeding which can lead to organ failure.

Ebola virus disease (EVD)

Image copyright Science Photo Library

Symptoms include high fever, bleeding and central nervous system damage

Fatality rate can reach 90% - but the current outbreak is about 55%

Incubation period is two to 21 days

There is no vaccine or cure

Supportive care such as rehydrating patients who have diarrhoea and vomiting can help recovery

Fruit bats are considered to be virus' natural host

Ebola: Experimental treatments

Why Ebola is so dangerous