A US doctor who contracted Ebola while working in Liberia and brought to the United States for treatment in a special isolation ward is said to be improving.
Dr Kent Brantly, a 33-year-old father of two young children, was able to walk with help from an ambulance after he was flown yesterday to Atlanta.
He is being treated by infectious disease specialists at Emory University Hospital.
Experts say it is too soon to predict whether Mr Brantly would survive.
Mr Brantly, who works for the North Carolina-based Christian organisation Samaritan's Purse, had been in Liberia responding to the worst Ebola outbreak on record when he contracted the disease.
Since February, more than 700 people in West Africa have died from the infection.
Ebola is a hemorrhagic virus with a death rate of up to 90% of those infected.
The fatality rate in the current epidemic is about 60%.
A second US aid worker who contracted Ebola alongside Dr Brantly, missionary Nancy Writebol, will be brought to the US on a later flight as the medical aircraft is equipped to carry only one patient at a time.
Standard treatment is to provide supportive care.
In Atlanta, doctors will try to maintain blood pressure and support breathing, with a respirator if needed, or provide dialysis if patients experience kidney failure, as some Ebola sufferers do.
Officials have said that Ms Writebol, a 59-year-old mother of two who worked to decontaminate those entering and leaving an Ebola isolation unit in Liberia, was expected to arrive this week in Atlanta.
Ms Writebol's husband, David, who had been living and working in Liberia with his wife, was expected to travel home separately within the next few days, their missionary organisation, SIMUSA, said in a statement.
The facility at Emory chosen to treat the two infected Americans, set up with the US Centers for Disease Control and Prevention, is one of four in the country with the ability to handle such cases.
The Americans will be treated primarily by a team of four infectious disease physicians, and will be able to see relatives through a plate-glass window and speak to them by phone or intercom.
It was unlikely that Dr Brantly's wife and children, who left Liberia before he began exhibiting symptoms, had contracted the disease because people who are exposed to Ebola but not yet sick cannot infect others.
The CDC was not aware of any Ebola patient being treated in the US previously, a spokeswoman has said.
Five people entered the country in the past decade with either Lassa Fever or Marburg, hemorrhagic fevers that are similar to Ebola.