Fire crews were called to the historic homestead in South Canterbury at 1.45pm, after reports of smoke coming from the two-storey building.
A Fire and Emergency New Zealand (Fenz) spokesman said there was "extensive damage" to the upstairs area of the 1913 homestead.
The back of the building had also been damaged, there was extensive water damage, and the overall structural condition of the building was yet to be determined.
Gary and Ann Dennison have owned Te Kiteroa since the 1980s, but lived overseas for a long time. They returned in 2007 and ran it as a bed and breakfast, more recently using it as a space for public talks, retreats and workshops.
In a statement yesterday, they said they still needed time to "take it all in", but thanked everyone for their support.
"We’re so thankful that despite the loss of property, no-one was injured.
"It means so much to have such a close knit and supportive community around us."
Many people had asked how they could help, but Mr and Mrs Dennison said their immediate needs were met.
"It is still early days and we are coming to terms with what has happened.
"In the coming days we will advise the community of our thoughts, and how, if you wish, you can support us and our vision at Te Kiteroa and the Point Bush Ecosanctuary."
At its peak, eight fire appliances, a command vehicle and three water tankers fought the fire. It had been largely extinguished by 5pm on Saturday and mopping-up efforts, including checking for hot spots, continued into the night.
A Fenz fire investigator had looked over the fire site, and further work was undertaken yesterday.
Because of the scale of the incident, the matter had been referred to the police, but the fire cause was currently viewed as undetermined rather than suspicious, a Fenz spokeswoman said.
Firefighters from Timaru were at the site yesterday to help remove historic furniture.
Te Kiteroa was due to host a Heritage Festival from May 25 to May 30, celebrating and commemorating the life of Emily Phillips, for whom the Edwardian property was built.
