The family of the Christian doctor who has contracted Ebola in Liberia have released a statement saying they believe God will heal him.

"As people with a deep faith in Jesus, we sincerely thank the thousands of people worldwide who have lifted up Kent and this dreadful situation in prayer. We continue to lean on that faith and take great consolation in our God in these times," the statement reads.

"We continue to believe that God will deliver Kent from this deadly virus.

"We have a strong family unit within a stronger faith community that has given us incredible support. Kent remains very physically weak, but his spirit has been determined throughout this ordeal."

Dr Kent Brantly moved to Monrovia, Liberia, with his wife and two young children last year as part of a two-year fellowship with Christian aid group Samaritan's Purse. He has been serving as Medical Director for the Ebola Consolidated Case Management Centre since the outbreak, and has now tested positive for the disease himself.

He is currently undergoing treatment at a Samaritan's Purse isolation centre, while his family have moved back to the US.

The virus, which proves fatal in 50-90 per cent of cases, has killed at least 672 people in Liberia, Guinea and Sierra Leone since March, according to the latest figures from the World Health Organisation (WHO).

Dr Brantly's family have asked for prayers for Kent and his co-worker, Nanacy Writebol, a second missionary to have contracted Ebola.

"We appreciate so much all the words of comfort and acts of kindness extended to our family," the statement adds.

"We ask for your continued prayers for Kent, his colleague Nancy Writebol and the healthcare workers in Liberia struggling to meet the overwhelming demands of those who are sick with the Ebola virus, as well as patients who have come to that hospital with other needs."