A British man who contracted the Ebola virus in Sierra Leone has arrived back in the UK on board an RAF jet.
The healthcare worker landed at London's RAF Northolt in a specially-equipped C-17 aircraft and has been transported to an isolation unit at the Royal Free Hospital in north London.
The man is "not currently seriously unwell", a Department of Health spokesman said.
Health officials have stressed the risk to the UK remains "very low".
The DoH said the decision to return the patient to the UK was taken following "clinical advice".
Prof John Watson, DoH deputy chief medical officer, said they would be taken in a specially adapted ambulance to a high level isolation unit - the only unit of its kind in the UK.
'Best care possible'
It is the first confirmed case of a Briton contracting the virus during the current outbreak, in which 1,427 people have died.
The World Health Organization has estimated 2,615 people in West Africa have been infected with Ebola since March.
Health officials reported the first cases outside West Africa - in the Democratic Republic of Congo - on Sunday.
The virus, for which there is no cure, is spread between humans through direct contact with infected bodily fluids. It is one of the world's deadliest diseases, with up to 90% of cases resulting in death.
A statement from Sierra Leone's health ministry said the Briton had been volunteering at a clinic in the Kenema district of the country.
Sidie Yayah Tunis, director of communications at the health ministry, said the patient had been flown out of the country's main airport in the town of Lungi on Sunday.
Dr Paul Cosford, director for health protection at Public Health England, said the man was being transferred with "all appropriate protocols promptly activated" by UK health agencies.
"Protective measures will be strictly maintained to minimise the risk of transmission to staff transporting the patient to the UK and healthcare workers treating the individual," he said.
He added: "UK hospitals have a proven record of dealing with imported infectious diseases and this patient will be isolated and will receive the best care possible."
Prof Watson said the UK had "robust, well-developed and well-tested NHS systems for managing unusual infectious diseases".
"It is important to be reassured that although a case of Ebola in a British national healthcare worker residing in Sierra Leone has been identified and is being brought back to the UK the overall risk to the public in the UK remains very low," he said.
Dr Bob Winter, from NHS England, said preparations had been under way over the past few weeks to ensure any patient being repatriated to the UK received the best possible care.
The unit at the Royal Free in the Hampstead area of London has been prepared to treat people with highly infectious diseases.
Patients can be treated in a special tent, which is part of a normal ward, BBC News correspondent Andy Moore said.
The tent ensures medical staff can interact with the patient, but are separated by either plastic or rubber. It has its own ventilation unit, which cleans air before it is released into the atmosphere.
It comes after two Americans recovered from Ebola and were last week discharged from hospital having been flown to the US and given an experimental drug.
Dr Kent Brantly, 33, and Nancy Writebol, 59, were flown from Liberia, in West Africa, to Atlanta, in the US, where they received an experimental treatment known as ZMapp.
Officials in Liberia have also said three medical staff have shown signs of improvement after taking the drug.
Health workers say the body has a greater chance of fighting off the virus if the patient seeks help fast and the symptoms are treated.
The Foreign Office this week issued updated travel advice, which urged Britons to assess the need to travel to Sierra Leone, Guinea and Liberia.
"General medical facilities throughout Sierra Leone are currently under severe strain due to the Ebola outbreak, and unable to provide the same standard of healthcare as in the UK," the travel advice said.
"Dedicated healthcare facilities for Ebola are overwhelmed."
Ebola Virus Disease (EVD)
- Symptoms include high fever, bleeding and central nervous system damage
- Fatality rate can reach 90% - but current outbreak has mortality rate of about 55%
- Incubation period is two to 21 days
- There is no vaccine or cure
- Supportive care such as rehydrating patients who have diarrhoea and vomiting can help recovery
- Fruit bats, a delicacy for some West Africans, are considered to be virus's natural host