Neighbours reported hearing "screams that somebody was on fire" before emergency services arrived.
"It's a horrible thing, especially on Christmas Day, for something to happen like that," one neighbour said.
Another neighbour said the couple lived with their four daughters.
Private security guards were yesterday guarding the property, which features a three-metre steel gate on its driveway.
A police investigation was under way.
Detective Senior Sergeant Dave de Lange of Hawke's Bay CIB said: "At this stage police have not been able to speak to this couple, so will be carrying out a scene examination at the Whakatu address and speaking with people who contacted emergency services regarding this event to begin to establish what happened.
"This matter is being investigated by police as serious injuries have occurred in circumstances that at this time are unexplained.
"A number of items of interest have been seized from the scene but these will need to be forensically tested by ESR before it can be established exactly what significance they have in relation to events that occurred at the Whakatu address and the relevance of these items in regard to the burns suffered by this couple."
A scene examination was undertaken yesterday by police, ESR and the NZ Fire Safety staff.
A St John Ambulance spokesperson said they went to the address after a 111 call. "They rang and said they needed an ambulance and just hung up."
Mr de Lange told Hawke's Bay Today that police had not yet determined what the woman was doing at the time she was burned.
He said CIB were involved because her injuries had the potential to cause death.
The burned woman was operated on at Middlemore Hospital last night before being transferred to intensive care.
Her partner was in a stable condition in a general ward at Hawke's Bay Hospital. Police had not yet spoken with him last night.
