US Ebola patient critical, hospital says

Ten colleagues of an American healthcare worker who is in a critical condition after contracting Ebola in Sierra Leone have been transferred to the US.

Hospital officials say a US healthcare worker who contracted Ebola is in a critical condition. (AAP)

The condition of an American healthcare worker who was sickened with Ebola in Sierra Leone has worsened and is now critical, hospital officials say.

The medical charity Partners in Health on Monday said the patient is a clinician who worked in the West African country, which along with Liberia and Guinea is struggling to emerge from the worst Ebola outbreak in history.

The patient was airlifted from Sierra Leone and was admitted to the National Institutes of Health Clinical Center on Friday.

"NIH physicians have changed the status of the patient with Ebola virus disease being treated at the NIH Clinical Center from serious to critical condition," a statement said.

"No additional details about the patient are being shared at this time."

Ten other healthcare workers "who came to the aid of their ailing colleague were subsequently identified as contacts of the evacuated clinician", Partners in Health said.

They are being transported to the United States and are being monitored for signs of illness.