A surgeon who travelled to Sierra Leone because he felt called by God to serve the sick in the latest Ebola outbreak has lost his fight against the virus.

Dr Martin Salia was infected while treating Ebola sufferers in Freetown and was flown back to the US, where he was a permanent resident, last week for specialist treatment.

He was taken in by the Nebraska Medical Center, which warned ahead of his arrival that although it had successfully treated a doctor and NBC cameraman for Ebola, Dr Salia was "possibly sicker".

The hospital confirmed that Dr Salia died shortly after 4am on Monday "as a result of the advanced symptoms of the disease".

Dr Phil Smith, medical director of the biocontainment unit told reporters: "Dr Salia was extremely critical when he arrived here, and unfortunately, despite our best efforts, we weren't able to save him."

Dr Salia was treated with ZMapp, the same experimental drug used successfully in the treatment of medical missionaries Dr Kent Brantly and Nancy Writebol.

Dr Smith continued: "We used every possible treatment available to give Dr Salia every possible opportunity for survival," Smith said. "As we have learned, early treatment with these patients is essential. In Dr Salia's case, his disease was already extremely advanced by the time he came here for treatment."

Dr Salia appeared in a recent video explaining that he had gone to Sierra Leone in spite of the dangers, because he believed it was "God's calling".

"There was just something inside of me, that the people in this part of Freetown needed help," he said.

"I see it as God's own desired framework for me. I took this job not because I want to but because I firmly believe it was a calling and God wanted me to.

"That's why I strongly believe that the God who has brought me here will fix whatever comes my way. I'm confident I just need to lean on him, trust him whatever comes in because he sent me here."

Watch the full clip below: