Kent Brantly, a doctor who was treating Ebola patients in Liberia, and Christian missionary worker Nancy Writebol, are both fighting for their lives after being stricken with the killer virus in west Africa.
Both are in serious but stable condition and are headed for special care isolation units at Emory University Hospital in Atlanta, Georgia, amid the worst outbreak of the virus in history.
Bruce Johnson, president of Service in Mission USA, the organization Writebol was working for, told CNN on Saturday the first flight ferrying one of the infected workers had left.
"The good news is we have confirmation that jet is in the air. I don't know the timeframe," Johnson said.
"It is encouraging it is in the air with one of them."
Reports later said Brantly was the first patient being flown back to the United States.
Both patients are being flown home on a Gulfstream private jet which had been fitted with a collapsible, mobile isolation unit designed to transfer employees from the US Centers for Disease Control and Prevention (CDC) exposed to contagious diseases.
When Brantly's jet arrives at a US Air Force base in Georgia later Saturday he will be transferred to Emory hospital's state-of-the-art isolation unit.
The unit is one of only four facilities in the United States and is located near the CDC headquarters in Atlanta.
"It is physically separate from other patient areas and has unique equipment and infrastructure that provide an extraordinarily high level of clinical isolation," Emory Healthcare said in a statement.
It is believed to be the first time a patient infected with Ebola has been treated anywhere in the United States.
The latest outbreak of the hemorrhagic fever in west Africa has killed 729 people of the more than 1,300 infected since March.
The World Health Organization has said the fast-moving outbreak was causing "catastrophic" loss of life in the affected countries of Guinea, Liberia, Nigeria and Sierra Leone.