The UN has warned that 20,000 people could be infected with Ebola by the end of 2014, and that the world is facing a huge funding challenge.

Nearly $US1.0 billion ($A1.1 billion) is needed to fight the Ebola outbreak raging in west Africa, the United Nations has said, warning that 20,000 could be infected by year end.

UN humanitarian chief Valerie Amos said there was a "huge funding challenge".

"If not dealt with effectively now, Ebola could become a major humanitarian crisis in countries currently affected," she told reporters in Geneva.

The capacity of Guinea, Sierra Leone and Liberia to provide even the most basic necessities was, she warned, "on the brink of collapse".

US President Barack Obama was set on Tuesday to announce US efforts to "turn the tide" in the Ebola epidemic, with plans to order 3000 US military personnel to west Africa.

US advisors will also train up to 500 health care providers per week in Liberia, according to the plan Obama was set to unveil in Atlanta.

The United Nations said the response to the crisis will require $US987.8 million, with about half needed for the worst-hit country, Liberia.

Its announcement comes amid mounting global alarm over the worst-ever Ebola epidemic, which by Friday had claimed 2461 lives out of 4985 cases, according to fresh numbers from the World Health Organization.

The UN document estimates that some 20,000 people could be infected with Ebola by the end of the year, with Guinea accounting for 16 per cent of infections, Sierra Leone 34 per cent and Liberia a full 40 per cent.

If the international community and affected countries respond swiftly and energetically, transmission should begin to slow by the end of the year and halt by mid-2015, the document said.

Copyright AAP 2014.