Doctors said Saturday the most recent Ebola patient to arrive for treatment in the United States was "extremely ill" and was receiving "maximum" care in efforts to save his life.

Martin Salia, a US resident who was infected with the deadly hemorrhagic fever while treating patients in his home country of Sierra Leone, was flown to the University of Nebraska Medical Center for treatment earlier in the day.

After a thorough examination, doctors there said Salia was in "extremely critical condition."

"This is an hour-by-hour situation," said Phil Smith, medical director of the biocontainment unit at UNMC, one of a handful of medical facilities in the United States specially designated to treat Ebola patients.

"He is extremely ill," Smith said, adding that experts were "targeting his most serious medical issues."

"Ebola produces symptoms that can obviously create a life-threatening situation for the patient," he said.

"We will do everything humanly possible to help him fight this disease."

There is no known cure for Ebola, one of the deadliest known pathogens, but trials for several possible treatments were announced this week in West Africa and Canada. The disease is spread through contact with bodily fluids.

More than 5,100 people are known to have died of the virus in West Africa and nearly 15,000 people have been infected in its deadliest ever outbreak -- most in Liberia, Sierra Leone and Guinea.

Salia is the third Ebola patient to be treated by the UNMC. Both of the previous patients survived.

His evacuation was facilitated by the US government at the request of his wife, an American citizen who agreed to reimburse all expenses, State Department spokeswoman Jen Psaki said in a statement.

Only one Ebola patient has died while under US treatment, Liberian man Thomas Eric Duncan.