A doctor from Sierra Leone infected with Ebola has been flown to the United States to be treated for the deadly virus, medical officials say.

The flight carrying Martin Salia left Sierra Leone’s capital Freetown early on Saturday, Brima Kargbo, the country’s chief medical officer said.

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The Nebraska Medical Centre in Omaha — one of a handful of medical facilities in the United States specially designated to treat Ebola patients — said he would arrive at around 5pm local time.

Salia, who has legal resident status in the US, had been treating Ebola patients at Freetown’s Connaught Hospital when he became infected.

His evacuation is being 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.

“Just as we have done in previous cases, every precaution is being taken to ensure the evacuation is completed safely and securely, that critical care is provided en route, and that strict isolation is maintained,” Psaki said.

Doctors have said they were told that Salia is “critically ill.”

Salia will be the third person treated for Ebola at the Nebraska Medical Centre. Both of the previous patients survived.

“We immediately started preparing the unit and notifying staff members of this possibility,” Phil Smith, bio-containment unit medical director, said in a statement.

“We’ve obviously been through this a couple of times before so we know what to expect.”

Nine people have been treated for the killer virus in the US but only one — Liberian-born Thomas Eric Duncan — has died from the disease.

The cases are part of the deadliest Ebola outbreak ever, which has killed more than 5100 people in West Africa and infected nearly 15,000 in total, mostly in Liberia, Sierra Leone and Guinea.