MONROVIA (AFP) -- The World Health Organization warned Monday that Liberia is set to see a huge spike in infections from the Ebola epidemic ravaging west Africa, with thousands of new cases imminent.

The UN agency said the country, worst-hit in the outbreak with almost 1,100 deaths, faced "many thousands" of new infections in the next three weeks.

"WHO and its director-general will continue to advocate for more Ebola treatment beds in Liberia and elsewhere, and will hold the world accountable for responding to this dire emergency with its unprecedented dimensions of human suffering," it said in a statement.

The deadliest Ebola epidemic the world has ever seen is spreading across west Africa, with Liberia, Guinea and Sierra Leone the worst affected.

The death toll has topped 2,000, out of nearly 4,000 people infected.

Key development partners trying to help Liberia respond to the outbreak "need to prepare to scale up their current efforts by three- to four-fold," the WHO said.

The countries bearing the brunt of the epidemic are among the world's poorest, with dilapidated medical infrastructures buckling under the strain.

Before the outbreak, Liberia had only one doctor to treat every 100,000 patients in a total population of 4.4 million people.

Now that 152 healthcare workers in the country have been infected and 79 have died, the WHO said the ratio had worsened significantly.

"Every infection or death of a doctor or nurse depletes response capacity significantly," it said.

The WHO said on Monday that one of its doctors in Sierra Leone had contracted the disease and would be evacuated.

The doctor, whose nationality was not given, is the second WHO staffer to be infected in the country. They were working at the Ebola treatment centre in Kenema, whose head doctor -- and the country's only virologist -- died from the virus in July.

Britain said it would open a new 62-bed centre outside Freetown in Sierra Leone within eight weeks. It will have 12 beds dedicated for local and international medical volunteers.

No Ebola treatment beds

The WHO described how taxis filled with entire families, including members suspected of having Ebola, criss-crossed the Liberian capital Monrovia "searching for a treatment bed".

"There are none. As WHO staff in Liberia confirm, no free beds for Ebola treatment exist anywhere in the country."

When Ebola patients are turned away from treatment centres, "they have no choice but to return to their communities and homes, where they inevitably infect others, perpetuating constantly higher flare-ups in the number of cases," it said.

In Montserrado county alone, which includes Monrovia, the agency said 1,000 beds were urgently needed to treat Ebola patients.

In the scramble to halt the contagion, some affected countries have quarantined whole regions. Several countries have stopped flights from affected areas.

African Union commission chief Nkosazana Dlamini-Zuma called Monday for travel bans to be lifted "to open up economic activities".

She told a crisis meeting in Addis Ababa there was an urgent need to "craft a united, comprehensive and collective African response", but warned "we must be careful not to introduce measures that may have more... social and economic impact than the disease itself".

Potential vaccine hope

Border restrictions are hampering trade and food prices are rising, Dlamini-Zuma said, echoing the UN's warning of serious foot shortages.

The CEOs of 11 firms operating in west Africa -- including ArcelorMittal and Randgold -- said in a joint statement that some measures were doing more harm than good.

"There is a risk the measures being taken to restrict travel to the countries most impacted by the virus will aggravate the growing humanitarian crisis," they said.

Despite the WHO's warning, the Liberian government said Monday it was lifting a quarantine on an Ebola hotspot near the country's international airport and reducing its night-time curfew by two hours.

The 17,000 residents of Dolo Town, 75 kilometres east of Monrovia, have been trapped since officials blockaded them in more than two weeks ago following a spike in cases.

Sierra Leone announced plans to visit every home in the country of six million to track down people with Ebola and remove dead bodies.

Ebola, transmitted through bodily fluids, leads to haemorrhagic fever and -- in over half of cases -- death. There is no specific treatment regime and no licensed vaccine.

Researchers reported in Nature Medicine on Monday that a vaccine tested on monkeys had provided "complete short-term and partial long-term protection".

The study endorsed testing the vaccine on humans, with first results due by the end of the year.